Leetcode problem 136 - Final Prices With a Special Discount in a Shop
You are given an integer array prices where prices[i] is the price of the ith item in a shop.
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Leetcode
Leetcode problem 135 - N-ary Tree Postorder Traversal
Given the root of an n-ary tree, return the postorder traversal of its nodes’ values.
Leetcode problem 134 - Increasing Order Search Tree
Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has ...
Leetcode problem 134 - Maximum Nesting Depth of the Parentheses
A string is a valid parentheses string (denoted VPS) if it meets one of the following:
Leetcode problem 133 - Minimum Number of Arrows to Burst Balloons
A valid parentheses string is either empty “”, “(“ + A + “)”, or A + B, where A and B are valid parentheses strings, and + represents string concatenation.
Leetcode problem 132 - Minimum Number of Arrows to Burst Balloons
There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array points where points...
Leetcode problem 131 - Insert Interval
You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and int...
Leetcode problem 130 - Merge Intervals
Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that c...
Leetcode problem 129 - Summary Ranges
You are given a sorted unique integer array nums.
Leetcode problem 128 - Longest Consecutive Sequence
Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
Leetcode problem 127 - Optimal Partition of String
Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a sin...
Leetcode problem 126 - Count Number of Distinct Integers After Reverse Operations
You are given an array nums consisting of positive integers.
Leetcode problem 125 - Minimum Number of Steps to Make Two Strings Anagram
You are given two strings of the same length s and t. In one step you can choose any character of t and replace it with another character.
Leetcode problem 124 - Arithmetic Subarrays
A sequence of numbers is called arithmetic if it consists of at least two elements, and the difference between every two consecutive elements is the same. Mo...
Leetcode problem 123 - Encode and Decode TinyURL
Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://lee...
Leetcode problem 122 - Sort the Students by Their Kth Score
There is a class with m students and n exams. You are given a 0-indexed m x n integer matrix score, where each row represents one student and score[i][j] den...
Leetcode problem 121 - Number of Laser Beams in a Bank
Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan of the bank, which is...
Leetcode problem 120 - Subrectangle Queries
Implement the class SubrectangleQueries which receives a rows x cols rectangle as a matrix of integers in the constructor and supports two methods:
Leetcode problem 119 - Find Missing and Repeated Values
You are given a 0-indexed 2D integer matrix grid of size n * n with values in the range [1, n2]. Each integer appears exactly once except a which appears twi...
Leetcode problem 118 - Row With Maximum Ones
Given a m x n binary matrix mat, find the 0-indexed position of the row that contains the maximum count of ones, and the number of ones in that row.
Leetcode problem 117 - Count Negative Numbers in a Sorted Matrix
Given a m x n matrix grid which is sorted in non-increasing order both row-wise and column-wise, return the number of negative numbers in grid.
Leetcode problem 116 - Delete Greatest Value in Each Row
You are given an m x n matrix grid consisting of positive integers.
Leetcode problem 115 - Matrix Diagonal Sum
Given a square matrix mat, return the sum of the matrix diagonals.
Leetcode problem 114 - Largest Local Values in a Matrix
You are given an n x n integer matrix grid.
Leetcode problem 113 - Richest Customer Wealth
You are given an m x n integer grid accounts where accounts[i][j] is the amount of money the ith customer has in the jth bank. ...
Leetcode problem 112 - Max Consecutive Ones III
Given a binary array nums and an integer k, return the maximum number of consecutive 1’s in the array if you can flip at most k 0’s.
Leetcode problem 111 - Count Complete Subarrays in an Array
You are given an array nums consisting of positive integers.
Leetcode problem 110 - Count Number of Nice Subarrays
Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it.
Leetcode problem 109 - Number of Substrings Containing All Three Characters
AGiven a string s consisting only of characters a, b and c.
Leetcode problem 108 - Maximize the Confusion of an Exam
A teacher is writing a test with n true/false questions, with ‘T’ denoting true and ‘F’ denoting false. He wants to confuse the students by maximizing the nu...
Leetcode problem 107 - Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold
Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.
Leetcode problem 106 - Find the K-Beauty of a Number
The k-beauty of an integer num is defined as the number of substrings of num when it is read as a string that meet the following conditions:
Leetcode problem 105 - Longest Nice Substring
A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, “abABB” is nice because ‘A’...
Leetcode problem 104 - Defuse the Bomb
You have a bomb to defuse, and your time is running out! Your informer will provide you with a circular array code of length of n and a key k.
Leetcode problem 103 - Substrings of Size Three with Distinct Characters
A string is good if there are no repeated characters.
Leetcode problem 102 - Maximum Strong Pair XOR I
You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition:
Leetcode problem 101 - Interval List Intersections
You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each list of i...
Leetcode problem 100 - Maximum Twin Sum of a Linked List
In a linked list of size n, where n is even, the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node, if 0 <= i <= (n / ...
Leetcode problem 99 - Rearrange Array Elements by Sign
You are given a 0-indexed integer array nums of even length consisting of an equal number of positive and negative integers.
Leetcode problem 98 - Partition Array According to Given Pivot
You are given a 0-indexed integer array nums and an integer pivot. Rearrange nums such that the following conditions are satisfied:
Leetcode problem 97 - Strictly Palindromic Number
An integer n is strictly palindromic if, for every base b between 2 and n - 2 (inclusive), the string representation of the integer n in base b is palindromi...
Leetcode problem 96 - Reverse String
Write a function that reverses a string. The input string is given as an array of characters s.
Leetcode problem 95 - Merge Strings Alternately
You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the othe...
Leetcode problem 94 - Find First Palindromic String in the Array
Given an array of strings words, return the first palindromic string in the array. If there is no such string, return an empty string “”.
Leetcode problem 93 - Reverse Prefix of Word
Given a 0-indexed string word and a character ch, reverse the segment of word that starts at index 0 and ends at the index of the first occurrence of ch (inc...
Leetcode problem 92 - Flipping an Image
Given an n x n binary matrix image, flip the image horizontally, then invert it, and return the resulting image.
Leetcode problem 91 - Reverse Words in a String III
Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
Leetcode problem 90 - Count Pairs Whose Sum is Less than Target
Given a 0-indexed integer array nums of length n and an integer target, return the number of pairs (i, j) where 0 <= i < j < n and nums[i] + nums[j]...
Leetcode problem 89 - Maximum Number of Coins You Can Get
There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:
Leetcode problem 88 - Max Increase to Keep City Skyline
There is a city composed of n x n blocks, where each block contains a single building shaped like a vertical square prism. You are given a 0-indexed n x n in...
Leetcode problem 87 - Partitioning Into Minimum Number Of Deci-Binary Numbers
A decimal number is called deci-binary if each of its digits is either 0 or 1 without any leading zeros. For example, 101 and 1100 are deci-binary, while 112...
Leetcode problem 86 - Minimum Time to Type Word Using Special Typewriter
There is a special typewriter with lowercase English letters ‘a’ to ‘z’ arranged in a circle with a pointer. A character can only be typed if the pointer is ...
Leetcode problem 85 - DI String Match
A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where:
Leetcode problem 84 - Array Partition
Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is m...
Leetcode problem 83 - Minimum Operations to Make the Array Increasing
You are given an integer array nums (0-indexed). In one operation, you can choose an element of the array and increment it by 1.
Leetcode problem 82 - Lexicographically Smallest Palindrome
You are given a string s consisting of lowercase English letters, and you are allowed to perform operations on it. In one operation, you can replace a charac...
Leetcode problem 81 - Maximum Sum With Exactly K Elements
You are given a 0-indexed integer array nums and an integer k. Your task is to perform the following operation exactly k times in order to maximize your scor...
Leetcode problem 80 - Maximum 69 Number
You are given a positive integer num consisting only of digits 6 and 9.
Leetcode problem 79 - Split a String in Balanced Strings
Balanced strings are those that have an equal quantity of ‘L’ and ‘R’ characters.
Leetcode problem 78 - Minimum Sum of Four Digit Number After Splitting Digits
You are given a positive integer num consisting of exactly four digits. Split num into two new integers new1 and new2 by using the digits found in num. Leadi...
Leetcode problem 77 - H-Index
Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper, return the researcher’s h-index.
Leetcode problem 76 - Rotate Array
You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0].
Leetcode problem 75 - Rotate Array
Given an integer array nums, rotate the array to the right by k steps, where k is non-negative.
Leetcode problem 74 - Majority Element
Given an array nums of size n, return the majority element.
Leetcode problem 73 - Remove Duplicates from Sorted Array II
Given an integer array nums sorted in non-decreasing order, remove some duplicates in-place such that each unique element appears at most twice. The relative...
Leetcode problem 72 - Remove Duplicates from Sorted Array
Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative orde...
Leetcode problem 71 - Merge Sorted Array
You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and ...
Leetcode problem 70 - Destination City
You are given the array paths, where paths[i] = [cityAi, cityBi] means there exists a direct path going from cityAi to cityBi. Return the destination city, t...
Leetcode problem 69 - Partition Labels
You are given a string s. We want to partition the string into as many parts as possible so that each letter appears in at most one part.
Leetcode problem 68 - Find the Prefix Common Array of Two Arrays
You are given two 0-indexed integer permutations A and B of length n.
Leetcode problem 67 - Finding the Users Active Minutes
You are given the logs for users’ actions on LeetCode, and an integer k. The logs are represented by a 2D integer array logs where each logs[i] = [IDi, timei...
Leetcode problem 66 - Find the Difference of Two Arrays
Given two 0-indexed integer arrays nums1 and nums2, return a list answer of size 2 where:
Leetcode problem 65 - Convert an Array Into a 2D Array With Conditions
You are given an integer array nums. You need to create a 2D array from nums satisfying the following conditions:
Leetcode problem 64 - Group the People Given the Group Size They Belong To
There are n people that are split into some unknown number of groups. Each person is labeled with a unique ID from 0 to n - 1.
Leetcode problem 63 - Find Maximum Number of String Pairs
You are given a 0-indexed array words consisting of distinct strings.
Leetcode problem 62 - Rings and Rods
There are n rings and each ring is either red, green, or blue. The rings are distributed across ten rods labeled from 0 to 9.
Leetcode problem 61 - Count the Number of Consistent Strings
You are given a string allowed consisting of distinct characters and an array of strings words. A string is consistent if all characters in the string appear...
Leetcode problem 60 - Unique Morse Code Words
International Morse Code defines a standard encoding where each letter is mapped to a series of dots and dashes, as follows:
Leetcode problem 59 - Check if the Sentence Is Pangram
A pangram is a sentence where every letter of the English alphabet appears at least once.
Leetcode problem 58 - Number of Arithmetic Triplets
You are given a 0-indexed, strictly increasing integer array nums and a positive integer diff. A triplet (i, j, k) is an arithmetic triplet if the following ...
Leetcode problem 57 - Decode the Message
You are given the strings key and message, which represent a cipher key and a secret message, respectively. The steps to decode message are as follows:
Leetcode problem 56 - Design an Ordered Stream
There is a stream of n (idKey, value) pairs arriving in an arbitrary order, where idKey is an integer between 1 and n and value is a string. No two pairs hav...
Leetcode problem 55 - Truncate Sentence
A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each of the words consists of only uppercase and lower...
Leetcode problem 54 - Check If Two String Arrays are Equivalent
Given two string arrays word1 and word2, return true if the two arrays represent the same string, and false otherwise.
Leetcode problem 53 - Count Items Matching a Rule
You are given an array items, where each items[i] = [typei, colori, namei] describes the type, color, and name of the ith item. You are also given a rule rep...
Leetcode problem 52 - Shuffle String
You are given a string s and an integer array indices of the same length. The string s will be shuffled such that the character at the ith position moves to ...
Leetcode problem 51 - Split a String in Balanced Strings
Balanced strings are those that have an equal quantity of ‘L’ and ‘R’ characters.
Leetcode problem 50 - Create Target Array in the Given Order
Given two arrays of integers nums and index. Your task is to create target array under the following rules:
Leetcode problem 49 - Count Pairs Whose Sum is Less than Target
Given a 0-indexed integer array nums of length n and an integer target, return the number of pairs (i, j) where 0 <= i < j < n and nums[i] + nums[j]...
Leetcode problem 48 - Smallest Even Multiple
Given a positive integer n, return the smallest positive integer that is a multiple of both 2 and n.
Leetcode problem 47 - Watering Plants
You want to water n plants in your garden with a watering can. The plants are arranged in a row and are labeled from 0 to n - 1 from left to right where the ...
Leetcode problem 46 - Best Time to Buy and Sell Stock2
You are given an integer array prices where prices[i] is the price of a given stock on the ith day.
Leetcode problem 45 - TwoSum
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
Leetcode problem 44 - Search Insert Position
Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were ...
Leetcode problem 43 - Jump Game
You are given an integer array nums. You are initially positioned at the array’s first index, and each element in the array represents your maximum jump leng...
Leetcode problem 42 - Valid Anagram
Given two strings s and t, return true if t is an anagram of s, and false otherwise.
Leetcode problem 41 - Subtract the Product and Sum of Digits of an Integer
Given an integer number n, return the difference between the product of its digits and the sum of its digits.
Leetcode problem 40 - How Many Numbers Are Smaller Than the Current Number
Given the array nums, for each nums[i] find out how many numbers in the array are smaller than it. That is, for each nums[i] you have to count the number of ...
Leetcode problem 39 - Left and Right Sum Differences
Given a 0-indexed integer array nums, find a 0-indexed integer array answer where:
Leetcode problem 38 - Maximum Number of Words Found in Sentences
A sentence is a list of words that are separated by a single space with no leading or trailing spaces.
Leetcode problem 37 - Goal Parser Interpretation
You own a Goal Parser that can interpret a string command. The command consists of an alphabet of “G”, “()” and/or “(al)” in some order. The Goal Parser will...
Leetcode problem 36 - Daily Leads and Partners
Table: DailySales
Leetcode problem 35 - Richest Customer Wealth
You are given an m x n integer grid accounts where accounts[i][j] is the amount of money the ith customer has in the jth bank. ...
Leetcode problem 34 - Kids With the Greatest Number of Candies
There are n kids with candies. You are given an integer array candies, where each candies[i] represents the number of candies the ith kid has, and an integer...
Leetcode problem 32 - Number of Good Pairs
Given an array of integers nums, return the number of good pairs.
Leetcode problem 31 - Jewels and Stones
You’re given strings jewels representing the types of stones that are jewels, and stones representing the stones you have. Each character in stones is a type...
Leetcode problem 30 - Final Value of Variable After Performing Operations
There is a programming language with only four operations and one variable X:
Leetcode problem 29 - Find the Maximum Achievable Number
You are given two integers, num and t.
Leetcode problem 28 - Shuffle the Array
Given the array nums consisting of 2n elements in the form [x1,x2,…,xn,y1,y2,…,yn].
Leetcode problem 27 - Convert the Temperature
You are given a non-negative floating point number rounded to two decimal places celsius, that denotes the temperature in Celsius.
Leetcode problem 26 - Defanging an IP Address
Given a valid (IPv4) IP address, return a defanged version of that IP address.
Leetcode problem 25 - Recyclable and Low Fat Products
Given an integer array nums of length n, you want to create an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] for 0 <= i < n ...
Leetcode problem 24 - Recyclable and Low Fat Products
Table: Products
Leetcode problem 23 - Build Array from Permutation
Given a zero-based permutation nums (0-indexed), build an array ans of the same length where ans[i] = nums[nums[i]] for each 0 <= i < nums.length and r...
Leetcode problem 22 - Number of Employees Who Met the Target
There are n employees in a company, numbered from 0 to n - 1. Each employee i has worked for hours[i] hours in the company.
Leetcode problem 21 - Contains Duplicate
Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.
Leetcode problem 20 - Palindrome Number
Given an integer x, return true if x is a palindrome, and false otherwise.
Leetcode problem 19 - Best Time to Buy and Sell Stock
You are given an array prices where prices[i] is the price of a given stock on the ith day.
Leetcode problem 18 - Single Number
Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.
Leetcode problem 17 - Merge Strings Alternately
You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the othe...
Leetcode problem 16 - Is Subsequence
Given two strings s and t, return true if s is a subsequence of t, or false otherwise.
Leetcode problem 15 - Move Zeroes
Given an integer array nums, move all 0’s to the end of it while maintaining the relative order of the non-zero elements.
Leetcode problem 14 - Can Place Flowers
You have a long flowerbed in which some of the plots are planted, and some are not. However, flowers cannot be planted in adjacent plots.
Leetcode problem 13 - Find the Index of the First Occurrence in a String
Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Leetcode problem 12 - Roman to Integer
Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.
Leetcode problem 11 - Majority Element
Given an array nums of size n, return the majority element.
Leetcode problem 10 - Climbing Stairs
You are climbing a staircase. It takes n steps to reach the top.
Leetcode problem 9 - Plus One
You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most ...
Leetcode problem 8 - Remove Element
Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the num...
30 Days of Javascript 14 - Execute Cancellable Function With Delay
Given a function fn, an array or arguments args, and a timeout t in milliseconds, return a cancel function cancelFn.
30 Days of Javascript 13 - Sleep
Given a positive integer millis, write an asynchronous function that sleeps for millis milliseconds. It can resolve any value.
30 Days of Javascript 12 - Add Two Promises
Given two promises promise1 and promise2, return a new promise. promise1 and promise2 will both resolve with a number. The returned promise should resolve wi...
30 Days of Javascript 11 - Memoize
Given a function fn, return a memoized version of that function.
30 Days of Javascript 9 - Return Length of Arguments Passed
Write a function argumentsLength that returns the count of arguments passed to it.
30 Days of Javascript 10 - Allow One Function Call
Given a function fn, return a new function that is identical to the original function except that it ensures fn is called at most once.
30 Days of Javascript 8 - Function Composition
Given an array of functions [f1, f2, f3, …, fn], return a new function fn that is the function composition of the array of functions.
30 Days of Javascript 7 - Array Reduce Transformation
Given an integer array nums, a reducer function fn, and an initial value init, return a reduced array.
30 Days of Javascript 6 - Array Reduce Transformation
Given an integer array arr and a filtering function fn, return a filtered array filteredArr.
30 Days of Javascript 5 - Apply Transform Over Each Element in Array
Given an integer array arr and a mapping function fn, return a new array with a transformation applied to each element.
30 Days of Javascript 4 - Counter2
Write a function createCounter. It should accept an initial integer init. It should return an object with three functions.
30 Days of Javascript 3 - To Be Or Not To Be
Write a function expect that helps developers test their code. It should take in any value val and return an object with the following two functions.
30 Days of Javascript 2 - Counter
Given an integer n, return a counter function. This counter function initially returns n and then returns 1 more than the previous value every subsequent tim...
30 Days of Javascript 1 - Create Hello World Function
Write a function createHelloWorld. It should return a new function that always returns “Hello World”.
Leetcode problem 7 - Ransom Note
Given two strings ransomNote and magazine, return true if ransomNote can be constructed by using the letters from magazine and false otherwise.
Leetcode problem 6 - Middle of the Linked List
Given the head of a singly linked list, return the middle node of the linked list.
Leetcode problem 5 - Number of Steps to Reduce a Number to Zero
Given an integer num, return the number of steps to reduce it to zero.
Leetcode problem 4 - Fizz Buzz
Fizz Buzz
FreeCodeCamp (Coding Interview) - Inventory Update
Inventory Update
Leetcode problem 3 - Longest Common Prefix
Longest Common Prefix
Leetcode problem 2 - Counter
Counter
Leetcode problem 1 - Valid Parentheses
Valid Parentheses
Array
Leetcode problem 136 - Final Prices With a Special Discount in a Shop
You are given an integer array prices where prices[i] is the price of the ith item in a shop.
Leetcode problem 133 - Minimum Number of Arrows to Burst Balloons
A valid parentheses string is either empty “”, “(“ + A + “)”, or A + B, where A and B are valid parentheses strings, and + represents string concatenation.
Leetcode problem 132 - Minimum Number of Arrows to Burst Balloons
There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array points where points...
Leetcode problem 131 - Insert Interval
You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and int...
Leetcode problem 130 - Merge Intervals
Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that c...
Leetcode problem 129 - Summary Ranges
You are given a sorted unique integer array nums.
Leetcode problem 126 - Count Number of Distinct Integers After Reverse Operations
You are given an array nums consisting of positive integers.
Leetcode problem 124 - Arithmetic Subarrays
A sequence of numbers is called arithmetic if it consists of at least two elements, and the difference between every two consecutive elements is the same. Mo...
Leetcode problem 122 - Sort the Students by Their Kth Score
There is a class with m students and n exams. You are given a 0-indexed m x n integer matrix score, where each row represents one student and score[i][j] den...
Leetcode problem 121 - Number of Laser Beams in a Bank
Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan of the bank, which is...
Leetcode problem 120 - Subrectangle Queries
Implement the class SubrectangleQueries which receives a rows x cols rectangle as a matrix of integers in the constructor and supports two methods:
Leetcode problem 119 - Find Missing and Repeated Values
You are given a 0-indexed 2D integer matrix grid of size n * n with values in the range [1, n2]. Each integer appears exactly once except a which appears twi...
Leetcode problem 118 - Row With Maximum Ones
Given a m x n binary matrix mat, find the 0-indexed position of the row that contains the maximum count of ones, and the number of ones in that row.
Leetcode problem 117 - Count Negative Numbers in a Sorted Matrix
Given a m x n matrix grid which is sorted in non-increasing order both row-wise and column-wise, return the number of negative numbers in grid.
Leetcode problem 116 - Delete Greatest Value in Each Row
You are given an m x n matrix grid consisting of positive integers.
Leetcode problem 115 - Matrix Diagonal Sum
Given a square matrix mat, return the sum of the matrix diagonals.
Leetcode problem 114 - Largest Local Values in a Matrix
You are given an n x n integer matrix grid.
Leetcode problem 113 - Richest Customer Wealth
You are given an m x n integer grid accounts where accounts[i][j] is the amount of money the ith customer has in the jth bank. ...
Leetcode problem 112 - Max Consecutive Ones III
Given a binary array nums and an integer k, return the maximum number of consecutive 1’s in the array if you can flip at most k 0’s.
Leetcode problem 111 - Count Complete Subarrays in an Array
You are given an array nums consisting of positive integers.
Leetcode problem 110 - Count Number of Nice Subarrays
Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it.
Leetcode problem 107 - Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold
Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.
Leetcode problem 104 - Defuse the Bomb
You have a bomb to defuse, and your time is running out! Your informer will provide you with a circular array code of length of n and a key k.
Leetcode problem 99 - Rearrange Array Elements by Sign
You are given a 0-indexed integer array nums of even length consisting of an equal number of positive and negative integers.
Leetcode problem 98 - Partition Array According to Given Pivot
You are given a 0-indexed integer array nums and an integer pivot. Rearrange nums such that the following conditions are satisfied:
Leetcode problem 94 - Find First Palindromic String in the Array
Given an array of strings words, return the first palindromic string in the array. If there is no such string, return an empty string “”.
Leetcode problem 92 - Flipping an Image
Given an n x n binary matrix image, flip the image horizontally, then invert it, and return the resulting image.
Leetcode problem 90 - Count Pairs Whose Sum is Less than Target
Given a 0-indexed integer array nums of length n and an integer target, return the number of pairs (i, j) where 0 <= i < j < n and nums[i] + nums[j]...
Leetcode problem 89 - Maximum Number of Coins You Can Get
There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:
Leetcode problem 85 - DI String Match
A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where:
Leetcode problem 84 - Array Partition
Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is m...
Leetcode problem 83 - Minimum Operations to Make the Array Increasing
You are given an integer array nums (0-indexed). In one operation, you can choose an element of the array and increment it by 1.
Leetcode problem 81 - Maximum Sum With Exactly K Elements
You are given a 0-indexed integer array nums and an integer k. Your task is to perform the following operation exactly k times in order to maximize your scor...
Java: Array
Array
String
Leetcode problem 134 - Maximum Nesting Depth of the Parentheses
A string is a valid parentheses string (denoted VPS) if it meets one of the following:
Leetcode problem 127 - Optimal Partition of String
Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a sin...
Leetcode problem 125 - Minimum Number of Steps to Make Two Strings Anagram
You are given two strings of the same length s and t. In one step you can choose any character of t and replace it with another character.
Leetcode problem 123 - Encode and Decode TinyURL
Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://lee...
Leetcode problem 121 - Number of Laser Beams in a Bank
Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan of the bank, which is...
Leetcode problem 109 - Number of Substrings Containing All Three Characters
AGiven a string s consisting only of characters a, b and c.
Leetcode problem 108 - Maximize the Confusion of an Exam
A teacher is writing a test with n true/false questions, with ‘T’ denoting true and ‘F’ denoting false. He wants to confuse the students by maximizing the nu...
Leetcode problem 106 - Find the K-Beauty of a Number
The k-beauty of an integer num is defined as the number of substrings of num when it is read as a string that meet the following conditions:
Leetcode problem 105 - Longest Nice Substring
A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, “abABB” is nice because ‘A’...
Leetcode problem 103 - Substrings of Size Three with Distinct Characters
A string is good if there are no repeated characters.
Leetcode problem 96 - Reverse String
Write a function that reverses a string. The input string is given as an array of characters s.
Leetcode problem 95 - Merge Strings Alternately
You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the othe...
Leetcode problem 94 - Find First Palindromic String in the Array
Given an array of strings words, return the first palindromic string in the array. If there is no such string, return an empty string “”.
Leetcode problem 93 - Reverse Prefix of Word
Given a 0-indexed string word and a character ch, reverse the segment of word that starts at index 0 and ends at the index of the first occurrence of ch (inc...
Leetcode problem 91 - Reverse Words in a String III
Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
Leetcode problem 88 - Max Increase to Keep City Skyline
There is a city composed of n x n blocks, where each block contains a single building shaped like a vertical square prism. You are given a 0-indexed n x n in...
Leetcode problem 87 - Partitioning Into Minimum Number Of Deci-Binary Numbers
A decimal number is called deci-binary if each of its digits is either 0 or 1 without any leading zeros. For example, 101 and 1100 are deci-binary, while 112...
Leetcode problem 86 - Minimum Time to Type Word Using Special Typewriter
There is a special typewriter with lowercase English letters ‘a’ to ‘z’ arranged in a circle with a pointer. A character can only be typed if the pointer is ...
Leetcode problem 85 - DI String Match
A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where:
Leetcode problem 82 - Lexicographically Smallest Palindrome
You are given a string s consisting of lowercase English letters, and you are allowed to perform operations on it. In one operation, you can replace a charac...
Leetcode problem 79 - Split a String in Balanced Strings
Balanced strings are those that have an equal quantity of ‘L’ and ‘R’ characters.
Javascript
Javascript - Linked Lists
Linked List
Javascript - Hash maps
Hash maps
Javascript - control flow
Control flow
30 Days of Javascript 14 - Execute Cancellable Function With Delay
Given a function fn, an array or arguments args, and a timeout t in milliseconds, return a cancel function cancelFn.
Javascript Promise
Promise
30 Days of Javascript 13 - Sleep
Given a positive integer millis, write an asynchronous function that sleeps for millis milliseconds. It can resolve any value.
Javascript Arrays
Array methods
30 Days of Javascript 12 - Add Two Promises
Given two promises promise1 and promise2, return a new promise. promise1 and promise2 will both resolve with a number. The returned promise should resolve wi...
30 Days of Javascript 11 - Memoize
Given a function fn, return a memoized version of that function.
30 Days of Javascript 9 - Return Length of Arguments Passed
Write a function argumentsLength that returns the count of arguments passed to it.
30 Days of Javascript 10 - Allow One Function Call
Given a function fn, return a new function that is identical to the original function except that it ensures fn is called at most once.
30 Days of Javascript 8 - Function Composition
Given an array of functions [f1, f2, f3, …, fn], return a new function fn that is the function composition of the array of functions.
30 Days of Javascript 7 - Array Reduce Transformation
Given an integer array nums, a reducer function fn, and an initial value init, return a reduced array.
30 Days of Javascript 6 - Array Reduce Transformation
Given an integer array arr and a filtering function fn, return a filtered array filteredArr.
30 Days of Javascript 5 - Apply Transform Over Each Element in Array
Given an integer array arr and a mapping function fn, return a new array with a transformation applied to each element.
30 Days of Javascript 4 - Counter2
Write a function createCounter. It should accept an initial integer init. It should return an object with three functions.
30 Days of Javascript 3 - To Be Or Not To Be
Write a function expect that helps developers test their code. It should take in any value val and return an object with the following two functions.
30 Days of Javascript 2 - Counter
Given an integer n, return a counter function. This counter function initially returns n and then returns 1 more than the previous value every subsequent tim...
30 Days of Javascript 1 - Create Hello World Function
Write a function createHelloWorld. It should return a new function that always returns “Hello World”.
React
Passport.js - mern-social-login project
TypeError: req.session.regenerate is not a function
JWT token - mern-auth project
JWT (Json Web Token)?
MERN project - To do app
Create react app named client in the root project folder using create-react-app command
MERN project - A project Manager
The project manager is for management of projects which user can add, view, edit and delete (CRUD functions) a project. This project is used React, bootstrap...
React: Initialize each application
Make components folder underneath src. And then, make a file named counter.jsx
React: Composing Components
Composing components
React: Passing event arguments
Passing event arguments
React: Increment a number
Increment a number
React: Refactor code
This is from counter app. render() { let classes = "bg m-2 bg-"; classes += this.state.count === 0 ? "warning" : "primary"; return ( &...
React: Render list of items
How to render list of items in React
React: Apply CSS
This posting will show you how to apply CSS in two ways, and this is what I learned applying CSS in react project so far. There are two ways more, but these ...
React: Using components
This posting is going to explain how to use components in React.
React: Count app
This is the project using react I want to learn. The purpose of the project is getting familiar with react and learning how to use react features on the proj...
React: How to use bootstrap with react?
I can use Bootstrap which allow front-end features easily while I’m building a react app. Open the terminal and type a below code. $ npm install bootstrap
React: Hello World
Hello World
React: Getting started
What is React? React is a declarative, efficient, and flexible JavaScript library for building user interfaces. It lets you compose complex UIs from small...
Greedy
Leetcode problem 133 - Minimum Number of Arrows to Burst Balloons
A valid parentheses string is either empty “”, “(“ + A + “)”, or A + B, where A and B are valid parentheses strings, and + represents string concatenation.
Leetcode problem 132 - Minimum Number of Arrows to Burst Balloons
There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array points where points...
Leetcode problem 127 - Optimal Partition of String
Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a sin...
Leetcode problem 89 - Maximum Number of Coins You Can Get
There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:
Leetcode problem 88 - Max Increase to Keep City Skyline
There is a city composed of n x n blocks, where each block contains a single building shaped like a vertical square prism. You are given a 0-indexed n x n in...
Leetcode problem 87 - Partitioning Into Minimum Number Of Deci-Binary Numbers
A decimal number is called deci-binary if each of its digits is either 0 or 1 without any leading zeros. For example, 101 and 1100 are deci-binary, while 112...
Leetcode problem 86 - Minimum Time to Type Word Using Special Typewriter
There is a special typewriter with lowercase English letters ‘a’ to ‘z’ arranged in a circle with a pointer. A character can only be typed if the pointer is ...
Leetcode problem 85 - DI String Match
A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where:
Leetcode problem 84 - Array Partition
Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is m...
Leetcode problem 83 - Minimum Operations to Make the Array Increasing
You are given an integer array nums (0-indexed). In one operation, you can choose an element of the array and increment it by 1.
Leetcode problem 82 - Lexicographically Smallest Palindrome
You are given a string s consisting of lowercase English letters, and you are allowed to perform operations on it. In one operation, you can replace a charac...
Leetcode problem 81 - Maximum Sum With Exactly K Elements
You are given a 0-indexed integer array nums and an integer k. Your task is to perform the following operation exactly k times in order to maximize your scor...
Leetcode problem 80 - Maximum 69 Number
You are given a positive integer num consisting only of digits 6 and 9.
Leetcode problem 79 - Split a String in Balanced Strings
Balanced strings are those that have an equal quantity of ‘L’ and ‘R’ characters.
Leetcode problem 78 - Minimum Sum of Four Digit Number After Splitting Digits
You are given a positive integer num consisting of exactly four digits. Split num into two new integers new1 and new2 by using the digits found in num. Leadi...
Hash Table
Leetcode problem 128 - Longest Consecutive Sequence
Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
Leetcode problem 127 - Optimal Partition of String
Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a sin...
Leetcode problem 126 - Count Number of Distinct Integers After Reverse Operations
You are given an array nums consisting of positive integers.
Leetcode problem 125 - Minimum Number of Steps to Make Two Strings Anagram
You are given two strings of the same length s and t. In one step you can choose any character of t and replace it with another character.
Leetcode problem 124 - Arithmetic Subarrays
A sequence of numbers is called arithmetic if it consists of at least two elements, and the difference between every two consecutive elements is the same. Mo...
Leetcode problem 123 - Encode and Decode TinyURL
Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://lee...
Leetcode problem 119 - Find Missing and Repeated Values
You are given a 0-indexed 2D integer matrix grid of size n * n with values in the range [1, n2]. Each integer appears exactly once except a which appears twi...
Leetcode problem 112 - Max Consecutive Ones III
Given a binary array nums and an integer k, return the maximum number of consecutive 1’s in the array if you can flip at most k 0’s.
Leetcode problem 111 - Count Complete Subarrays in an Array
You are given an array nums consisting of positive integers.
Leetcode problem 110 - Count Number of Nice Subarrays
Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it.
Leetcode problem 109 - Number of Substrings Containing All Three Characters
AGiven a string s consisting only of characters a, b and c.
Leetcode problem 105 - Longest Nice Substring
A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, “abABB” is nice because ‘A’...
Leetcode problem 103 - Substrings of Size Three with Distinct Characters
A string is good if there are no repeated characters.
Leetcode problem 102 - Maximum Strong Pair XOR I
You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition:
Matrix
Leetcode problem 122 - Sort the Students by Their Kth Score
There is a class with m students and n exams. You are given a 0-indexed m x n integer matrix score, where each row represents one student and score[i][j] den...
Leetcode problem 121 - Number of Laser Beams in a Bank
Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan of the bank, which is...
Leetcode problem 120 - Subrectangle Queries
Implement the class SubrectangleQueries which receives a rows x cols rectangle as a matrix of integers in the constructor and supports two methods:
Leetcode problem 119 - Find Missing and Repeated Values
You are given a 0-indexed 2D integer matrix grid of size n * n with values in the range [1, n2]. Each integer appears exactly once except a which appears twi...
Leetcode problem 118 - Row With Maximum Ones
Given a m x n binary matrix mat, find the 0-indexed position of the row that contains the maximum count of ones, and the number of ones in that row.
Leetcode problem 117 - Count Negative Numbers in a Sorted Matrix
Given a m x n matrix grid which is sorted in non-increasing order both row-wise and column-wise, return the number of negative numbers in grid.
Leetcode problem 116 - Delete Greatest Value in Each Row
You are given an m x n matrix grid consisting of positive integers.
Leetcode problem 115 - Matrix Diagonal Sum
Given a square matrix mat, return the sum of the matrix diagonals.
Leetcode problem 114 - Largest Local Values in a Matrix
You are given an n x n integer matrix grid.
Leetcode problem 113 - Richest Customer Wealth
You are given an m x n integer grid accounts where accounts[i][j] is the amount of money the ith customer has in the jth bank. ...
Leetcode problem 92 - Flipping an Image
Given an n x n binary matrix image, flip the image horizontally, then invert it, and return the resulting image.
Leetcode problem 88 - Max Increase to Keep City Skyline
There is a city composed of n x n blocks, where each block contains a single building shaped like a vertical square prism. You are given a 0-indexed n x n in...
Two pointers
Leetcode problem 101 - Interval List Intersections
You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each list of i...
Leetcode problem 100 - Maximum Twin Sum of a Linked List
In a linked list of size n, where n is even, the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node, if 0 <= i <= (n / ...
Leetcode problem 99 - Rearrange Array Elements by Sign
You are given a 0-indexed integer array nums of even length consisting of an equal number of positive and negative integers.
Leetcode problem 98 - Partition Array According to Given Pivot
You are given a 0-indexed integer array nums and an integer pivot. Rearrange nums such that the following conditions are satisfied:
Leetcode problem 97 - Strictly Palindromic Number
An integer n is strictly palindromic if, for every base b between 2 and n - 2 (inclusive), the string representation of the integer n in base b is palindromi...
Leetcode problem 96 - Reverse String
Write a function that reverses a string. The input string is given as an array of characters s.
Leetcode problem 95 - Merge Strings Alternately
You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the othe...
Leetcode problem 94 - Find First Palindromic String in the Array
Given an array of strings words, return the first palindromic string in the array. If there is no such string, return an empty string “”.
Leetcode problem 93 - Reverse Prefix of Word
Given a 0-indexed string word and a character ch, reverse the segment of word that starts at index 0 and ends at the index of the first occurrence of ch (inc...
Leetcode problem 92 - Flipping an Image
Given an n x n binary matrix image, flip the image horizontally, then invert it, and return the resulting image.
Leetcode problem 91 - Reverse Words in a String III
Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
Leetcode problem 90 - Count Pairs Whose Sum is Less than Target
Given a 0-indexed integer array nums of length n and an integer target, return the number of pairs (i, j) where 0 <= i < j < n and nums[i] + nums[j]...
Sliding Window
Leetcode problem 112 - Max Consecutive Ones III
Given a binary array nums and an integer k, return the maximum number of consecutive 1’s in the array if you can flip at most k 0’s.
Leetcode problem 111 - Count Complete Subarrays in an Array
You are given an array nums consisting of positive integers.
Leetcode problem 110 - Count Number of Nice Subarrays
Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it.
Leetcode problem 109 - Number of Substrings Containing All Three Characters
AGiven a string s consisting only of characters a, b and c.
Leetcode problem 108 - Maximize the Confusion of an Exam
A teacher is writing a test with n true/false questions, with ‘T’ denoting true and ‘F’ denoting false. He wants to confuse the students by maximizing the nu...
Leetcode problem 107 - Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold
Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.
Leetcode problem 106 - Find the K-Beauty of a Number
The k-beauty of an integer num is defined as the number of substrings of num when it is read as a string that meet the following conditions:
Leetcode problem 105 - Longest Nice Substring
A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, “abABB” is nice because ‘A’...
Leetcode problem 104 - Defuse the Bomb
You have a bomb to defuse, and your time is running out! Your informer will provide you with a circular array code of length of n and a key k.
Leetcode problem 103 - Substrings of Size Three with Distinct Characters
A string is good if there are no repeated characters.
Leetcode problem 102 - Maximum Strong Pair XOR I
You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition:
Sorting
Leetcode problem 133 - Minimum Number of Arrows to Burst Balloons
A valid parentheses string is either empty “”, “(“ + A + “)”, or A + B, where A and B are valid parentheses strings, and + represents string concatenation.
Leetcode problem 132 - Minimum Number of Arrows to Burst Balloons
There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array points where points...
Leetcode problem 130 - Merge Intervals
Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that c...
Leetcode problem 124 - Arithmetic Subarrays
A sequence of numbers is called arithmetic if it consists of at least two elements, and the difference between every two consecutive elements is the same. Mo...
Leetcode problem 122 - Sort the Students by Their Kth Score
There is a class with m students and n exams. You are given a 0-indexed m x n integer matrix score, where each row represents one student and score[i][j] den...
Leetcode problem 116 - Delete Greatest Value in Each Row
You are given an m x n matrix grid consisting of positive integers.
Leetcode problem 90 - Count Pairs Whose Sum is Less than Target
Given a 0-indexed integer array nums of length n and an integer target, return the number of pairs (i, j) where 0 <= i < j < n and nums[i] + nums[j]...
Leetcode problem 89 - Maximum Number of Coins You Can Get
There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:
Leetcode problem 84 - Array Partition
Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is m...
Leetcode problem 78 - Minimum Sum of Four Digit Number After Splitting Digits
You are given a positive integer num consisting of exactly four digits. Split num into two new integers new1 and new2 by using the digits found in num. Leadi...
Math
Leetcode problem 126 - Count Number of Distinct Integers After Reverse Operations
You are given an array nums consisting of positive integers.
Leetcode problem 121 - Number of Laser Beams in a Bank
Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan of the bank, which is...
Leetcode problem 119 - Find Missing and Repeated Values
You are given a 0-indexed 2D integer matrix grid of size n * n with values in the range [1, n2]. Each integer appears exactly once except a which appears twi...
Leetcode problem 110 - Count Number of Nice Subarrays
Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it.
Leetcode problem 106 - Find the K-Beauty of a Number
The k-beauty of an integer num is defined as the number of substrings of num when it is read as a string that meet the following conditions:
Leetcode problem 97 - Strictly Palindromic Number
An integer n is strictly palindromic if, for every base b between 2 and n - 2 (inclusive), the string representation of the integer n in base b is palindromi...
Leetcode problem 89 - Maximum Number of Coins You Can Get
There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:
Leetcode problem 80 - Maximum 69 Number
You are given a positive integer num consisting only of digits 6 and 9.
Leetcode problem 78 - Minimum Sum of Four Digit Number After Splitting Digits
You are given a positive integer num consisting of exactly four digits. Split num into two new integers new1 and new2 by using the digits found in num. Leadi...
Stack
Leetcode problem 136 - Final Prices With a Special Discount in a Shop
You are given an integer array prices where prices[i] is the price of the ith item in a shop.
Leetcode problem 135 - N-ary Tree Postorder Traversal
Given the root of an n-ary tree, return the postorder traversal of its nodes’ values.
Leetcode problem 134 - Increasing Order Search Tree
Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has ...
Leetcode problem 134 - Maximum Nesting Depth of the Parentheses
A string is a valid parentheses string (denoted VPS) if it meets one of the following:
Leetcode problem 100 - Maximum Twin Sum of a Linked List
In a linked list of size n, where n is even, the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node, if 0 <= i <= (n / ...
MERN
Passport.js - mern-social-login project
TypeError: req.session.regenerate is not a function
JWT token - mern-auth project
JWT (Json Web Token)?
MERN project - To do app
Create react app named client in the root project folder using create-react-app command
MERN project - A project Manager
The project manager is for management of projects which user can add, view, edit and delete (CRUD functions) a project. This project is used React, bootstrap...
Node.js
Passport.js - mern-social-login project
TypeError: req.session.regenerate is not a function
JWT token - mern-auth project
JWT (Json Web Token)?
MERN project - To do app
Create react app named client in the root project folder using create-react-app command
MERN project - A project Manager
The project manager is for management of projects which user can add, view, edit and delete (CRUD functions) a project. This project is used React, bootstrap...
Mongo DB
Passport.js - mern-social-login project
TypeError: req.session.regenerate is not a function
JWT token - mern-auth project
JWT (Json Web Token)?
MERN project - To do app
Create react app named client in the root project folder using create-react-app command
MERN project - A project Manager
The project manager is for management of projects which user can add, view, edit and delete (CRUD functions) a project. This project is used React, bootstrap...
Express
Passport.js - mern-social-login project
TypeError: req.session.regenerate is not a function
JWT token - mern-auth project
JWT (Json Web Token)?
MERN project - To do app
Create react app named client in the root project folder using create-react-app command
MERN project - A project Manager
The project manager is for management of projects which user can add, view, edit and delete (CRUD functions) a project. This project is used React, bootstrap...
Postgresql
How to re-create postgresql database in render.com
Render provides free plan for PostgreSQL, but there is a time limit for free plan. I can use it only for 3 month which means I need to recreate every 3 month...
Postgresql datatype
Datatype
Postgresql
What is PostgreSQL?
Postgresql commands
I’ve collected some useful commands for capitalizing on postgresql. It’s going to keep updating whenever I found a command I need.
Simulation
Leetcode problem 116 - Delete Greatest Value in Each Row
You are given an m x n matrix grid consisting of positive integers.
Leetcode problem 99 - Rearrange Array Elements by Sign
You are given a 0-indexed integer array nums of even length consisting of an equal number of positive and negative integers.
Leetcode problem 98 - Partition Array According to Given Pivot
You are given a 0-indexed integer array nums and an integer pivot. Rearrange nums such that the following conditions are satisfied:
Leetcode problem 92 - Flipping an Image
Given an n x n binary matrix image, flip the image horizontally, then invert it, and return the resulting image.
HTML
HTML & HTML5: Basic
This posting is for getting used to HTML & HTML5.
Markup vs Markdown languages
Markup language Markup Language is a type of language that defines rules for indicating the format in which documents are displayed on the screen or speci...
Counting
Leetcode problem 125 - Minimum Number of Steps to Make Two Strings Anagram
You are given two strings of the same length s and t. In one step you can choose any character of t and replace it with another character.
Leetcode problem 103 - Substrings of Size Three with Distinct Characters
A string is good if there are no repeated characters.
Leetcode problem 79 - Split a String in Balanced Strings
Balanced strings are those that have an equal quantity of ‘L’ and ‘R’ characters.
Bit Manipulation
Leetcode problem 105 - Longest Nice Substring
A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, “abABB” is nice because ‘A’...
Leetcode problem 102 - Maximum Strong Pair XOR I
You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition:
Leetcode problem 92 - Flipping an Image
Given an n x n binary matrix image, flip the image horizontally, then invert it, and return the resulting image.
Markdown
Syntax of markdown
Heading Heading1 Heading2 Heading3 Heading4 Heading5 Heading6
Markup vs Markdown languages
Markup language Markup Language is a type of language that defines rules for indicating the format in which documents are displayed on the screen or speci...
Bootstrap
Bootstrap: Basic
This page will be my journal learning bootstrap responsive CSS framework.
React: How to use bootstrap with react?
I can use Bootstrap which allow front-end features easily while I’m building a react app. Open the terminal and type a below code. $ npm install bootstrap
CSS
CSS Display preperty
Property Values
React: Apply CSS
This posting will show you how to apply CSS in two ways, and this is what I learned applying CSS in react project so far. There are two ways more, but these ...
SAIT
Back to top ↑Blog
Back to top ↑CORS
CORS policy
The problem I had while developing - Cross Origin Resource Sharing (CORS)
Two Pointers
Leetcode problem 85 - DI String Match
A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where:
Leetcode problem 82 - Lexicographically Smallest Palindrome
You are given a string s consisting of lowercase English letters, and you are allowed to perform operations on it. In one operation, you can replace a charac...
Binary Search
Leetcode problem 117 - Count Negative Numbers in a Sorted Matrix
Given a m x n matrix grid which is sorted in non-increasing order both row-wise and column-wise, return the number of negative numbers in grid.
Leetcode problem 108 - Maximize the Confusion of an Exam
A teacher is writing a test with n true/false questions, with ‘T’ denoting true and ‘F’ denoting false. He wants to confuse the students by maximizing the nu...
Design
Leetcode problem 123 - Encode and Decode TinyURL
Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://lee...
Leetcode problem 120 - Subrectangle Queries
Implement the class SubrectangleQueries which receives a rows x cols rectangle as a matrix of integers in the constructor and supports two methods:
Tree
Leetcode problem 135 - N-ary Tree Postorder Traversal
Given the root of an n-ary tree, return the postorder traversal of its nodes’ values.
Leetcode problem 134 - Increasing Order Search Tree
Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has ...
Depth-First Search
Leetcode problem 135 - N-ary Tree Postorder Traversal
Given the root of an n-ary tree, return the postorder traversal of its nodes’ values.
Leetcode problem 134 - Increasing Order Search Tree
Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has ...
Java
Java: Array
Array
Initial setting
React: Getting started
What is React? React is a declarative, efficient, and flexible JavaScript library for building user interfaces. It lets you compose complex UIs from small...
Setting
React: Getting started
What is React? React is a declarative, efficient, and flexible JavaScript library for building user interfaces. It lets you compose complex UIs from small...
Markup
Markup vs Markdown languages
Markup language Markup Language is a type of language that defines rules for indicating the format in which documents are displayed on the screen or speci...
Hello World
React: Hello World
Hello World
Count app
React: Count app
This is the project using react I want to learn. The purpose of the project is getting familiar with react and learning how to use react features on the proj...
Components
React: Using components
This posting is going to explain how to use components in React.
List of items
React: Render list of items
How to render list of items in React
array
React: Render list of items
How to render list of items in React
Refactor
React: Refactor code
This is from counter app. render() { let classes = "bg m-2 bg-"; classes += this.state.count === 0 ? "warning" : "primary"; return ( &...
onClick()
React: Increment a number
Increment a number
Composing
React: Composing Components
Composing components
AWS
AWS: Installation of RDS
What is RDS?
RDS
AWS: Installation of RDS
What is RDS?
HTML5
HTML & HTML5: Basic
This posting is for getting used to HTML & HTML5.
layout
CSS Display preperty
Property Values
JWT
JWT token - mern-auth project
JWT (Json Web Token)?
Passport.js
Passport.js - mern-social-login project
TypeError: req.session.regenerate is not a function
Netlify
Deploy web app with netlify and heroku
I’m going to deploy my web application with Netlify and Heroku which provide free plan for an individual project. These can be alternative way to show my pro...
Heroku
Deploy web app with netlify and heroku
I’m going to deploy my web application with Netlify and Heroku which provide free plan for an individual project. These can be alternative way to show my pro...
Deployment
Deploy web app with netlify and heroku
I’m going to deploy my web application with Netlify and Heroku which provide free plan for an individual project. These can be alternative way to show my pro...
commands
Postgresql commands
I’ve collected some useful commands for capitalizing on postgresql. It’s going to keep updating whenever I found a command I need.
Postgresql datatype
Postgresql datatype
Datatype
render
How to re-create postgresql database in render.com
Render provides free plan for PostgreSQL, but there is a time limit for free plan. I can use it only for 3 month which means I need to recreate every 3 month...
Trouble shooting
Back to top ↑Arrays
Javascript Arrays
Array methods
Promise
Javascript Promise
Promise
Python
Python - Variable
Python is dynamically typed, which means I don’t need to explicitly declare the data type of a variable. Python will infer the data type based on the assigne...
web worker, Javascript
Web workers in JS
Web workers
Counting Sort
Leetcode problem 84 - Array Partition
Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is m...
Game Theory
Leetcode problem 89 - Maximum Number of Coins You Can Get
There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:
Linked List
Leetcode problem 100 - Maximum Twin Sum of a Linked List
In a linked list of size n, where n is even, the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node, if 0 <= i <= (n / ...
Trie
Leetcode problem 102 - Maximum Strong Pair XOR I
You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition:
Divide and Conquer
Leetcode problem 105 - Longest Nice Substring
A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, “abABB” is nice because ‘A’...
Prefix Sum
Leetcode problem 108 - Maximize the Confusion of an Exam
A teacher is writing a test with n true/false questions, with ‘T’ denoting true and ‘F’ denoting false. He wants to confuse the students by maximizing the nu...
Heap
Leetcode problem 116 - Delete Greatest Value in Each Row
You are given an m x n matrix grid consisting of positive integers.
Hash Function
Leetcode problem 123 - Encode and Decode TinyURL
Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://lee...
Union Find
Leetcode problem 128 - Longest Consecutive Sequence
Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
Binary Search Tree
Leetcode problem 134 - Increasing Order Search Tree
Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has ...
Binary Tree
Leetcode problem 134 - Increasing Order Search Tree
Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has ...
Monotonic Stack
Leetcode problem 136 - Final Prices With a Special Discount in a Shop
You are given an integer array prices where prices[i] is the price of the ith item in a shop.