LeetCode in Kotlin

2629. Function Composition

Easy

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

Solution

type F = (x: number) => number

function compose(functions: F[]): F {
    return function (x) {
        if (functions.length == 0) return x
        for (let ind = functions.length - 1; ind >= 0; ind--) {
            x = functions[ind](x)
        }
        return x
    }
}

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

export { compose }

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