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.

A reduced array is created by applying the following operation: val = fn(init, nums[0]), val = fn(val, nums[1]), val = fn(val, nums[2]), … until every element in the array has been processed. The final value of val is returned.

If the length of the array is 0, it should return init.

Please solve it without using the built-in Array.reduce method.

Example 1:

Input: nums = [1,2,3,4] fn = function sum(accum, curr) { return accum + curr; } init = 0 Output: 10 Explanation: initially, the value is init=0. (0) + nums[0] = 1 (1) + nums[1] = 3 (3) + nums[2] = 6 (6) + nums[3] = 10 The final answer is 10. Example 2:

Input: nums = [1,2,3,4] fn = function sum(accum, curr) { return accum + curr * curr; } init = 100 Output: 130 Explanation: initially, the value is init=100. (100) + nums[0]^2 = 101 (101) + nums[1]^2 = 105 (105) + nums[2]^2 = 114 (114) + nums[3]^2 = 130 The final answer is 130. Example 3:

Input: nums = [] fn = function sum(accum, curr) { return 0; } init = 25 Output: 25 Explanation: For empty arrays, the answer is always init.

/**
 * @param {number[]} nums
 * @param {Function} fn
 * @param {number} init
 * @return {number}
 */
var reduce = function (nums, fn, init) {
  let curVal = init;
  for (let i = 0; i < nums.length; i++) {
    curVal = fn(curVal, nums[i]);
  }
  return curVal;
};

The reduce function takes three parameters: nums, which is the array to be reduced, fn, which is the callback function, and init, which is the initial value. Inside the reduce function, a variable curVal is declared and assigned the value of init. This variable will hold the accumulated value during the reduction process. A for loop is used to iterate over each element of the nums array. Within each iteration of the loop, the callback function fn is called with two arguments: the current accumulated value (curVal) and the current element of the nums array (nums[i]). The result of the callback function is assigned to the curVal variable, overwriting the previous accumulated value. After iterating over all elements of the nums array, the final accumulated value (curVal) is returned as the result of the reduce function.