08_functionComposition.js

// Question Link: https://leetcode.com/problems/function-composition/description/?envType=study-plan-v2&envId=30-days-of-javascript
// Solution Link: https://leetcode.com/problems/function-composition/solutions/5434884/javascript-easy-solution-using-for-loop-tc-o-n-sc-o-1/


/*
2629. 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.
The function composition of [f(x), g(x), h(x)] is fn(x) = f(g(h(x))).
The function composition of an empty list of functions is the identity function f(x) = x.

You may assume each function in the array accepts one integer as input and returns one integer as output.

Example 1:
Input: functions = [x => x + 1, x => x * x, x => 2 * x], x = 4
Output: 65
Explanation:
Evaluating from right to left ...
Starting with x = 4.
2 * (4) = 8
(8) * (8) = 64
(64) + 1 = 65

Example 2:
Input: functions = [x => 10 * x, x => 10 * x, x => 10 * x], x = 1
Output: 1000
Explanation:
Evaluating from right to left ...
10 * (1) = 10
10 * (10) = 100
10 * (100) = 1000

Example 3:
Input: functions = [], x = 42
Output: 42
Explanation:
The composition of zero functions is the identity function
 
Constraints:
-1000 <= x <= 1000
0 <= functions.length <= 1000
all functions accept and return a single integer
*/



/**
 * @param {Function[]} functions
 * @return {Function}
 */
var compose = function(functions) {
    
    return function(x) {
        let result = x;

        for (let i = functions.length - 1; i >= 0; i--) {
            result = functions[i](result);
        }

        return result;
    }
};

/**
 * const fn = compose([x => x + 1, x => 2 * x])
 * fn(4) // 9
 */