javascript 数组变为未定义

Question

Input: nums = [1,2,3,4] Output: [1,3,6,10] Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4] .

var runningSum = function(nums) {
    const array = new Array (nums.length);
    array[0] = nums[0];
    for( let i=1; i<nums.length; i++){
        array[i] = nums[i] + array[i-1]
    }
};

the result turns out to be undefine, I don't know where I did wrong.

Answer 1

You have to return the array

so

var runningSum = function(nums) {
    const array = new Array (nums.length);
    array[0] = nums[0];
    for( let i=1; i<nums.length; i++){
        array[i] = nums[i] + array[i-1]
    }
    return array;
};

instead of

var runningSum = function(nums) {
    const array = new Array (nums.length);
    array[0] = nums[0];
    for( let i=1; i<nums.length; i++){
        array[i] = nums[i] + array[i-1]
    }
};

Answer 2

Here is another approach to solve the problem using recursion.

 const nums = [1, 2, 3, 4]; const runningSum = (arr, result = [], sum = 0) => { if (arr.length === 0) return result; const tmp = sum + arr.shift(); result.push(tmp); return runningSum(arr, result, tmp); }; console.log(runningSum(nums));