2635-ApplyTransformOverEachElementInArray.js

// 2635. 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.

// The returned array should be created such that returnedArray[i] = fn(arr[i], i).

// Please solve it without the built-in Array.map method.

// Example 1:
// Input: arr = [1,2,3], fn = function plusone(n) { return n + 1; }
// Output: [2,3,4]
// Explanation:
//     const newArray = map(arr, plusone); // [2,3,4]
//     The function increases each value in the array by one. 

// Example 2:
// Input: arr = [1,2,3], fn = function plusI(n, i) { return n + i; }
// Output: [1,3,5]
// Explanation: The function increases each value by the index it resides in.

// Example 3:
// Input: arr = [10,20,30], fn = function constant() { return 42; }
// Output: [42,42,42]
// Explanation: The function always returns 42.

// Constraints:
//         0 <= arr.length <= 1000
//         -109 <= arr[i] <= 109
//         fn returns a number

/**
 * @param {number[]} arr
 * @param {Function} fn
 * @return {number[]}
 */
var map = function(arr, fn) {
    let res = [];
    for (let i = 0; i < arr.length; i++) {
       res.push(fn(arr[i],i));
    }
    return res;
};

// use reduce
var map = function(arr, fn) {
    const res=[]
    arr.reduce((accum,curr,index)=>{
        accum.push(fn(curr,index))
        return accum
    },res)

    return res
};