2626. Array Reduce Transformation

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# 題目敘述

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.

# Solution

/**

 * @param {number[]} nums

 * @param {Function} fn

 * @param {number} init

 * @return {number}

 */

var reduce = function(nums, fn, init) {

    nums.forEach(num => init = fn(init, num));

    return init;

};

type Fn = (accum: number, curr: number) => number

function reduce(nums: number[], fn: Fn, init: number): number {

    nums.forEach(num => init = fn(init, num));

    return init;

};