在Javascript中运行输入数组的总和

Question

I want to build a function that

1. takes an array of numbers as an input.
2. calculates the running sum of the numbers in the input array.
3. returns a new array that contains the running sum.

For example, if I call this function with the input of [1,2,3,4], the output should be [1,3,6,10]. However, when I run my code, it returns an empty array.

The following is the code I got so far.

 function sumOfArray(nums) { var output = []; // tip: initialize like let output = [nums?.[0] ?? 0]; for(let i = 1 ; i < nums.length ; i++) { nums[i] = nums[i] + nums[i-1]; output.push(nums[i]); } return output; }; console.log( 'calling sumOfArray([1,2,3,4])', sumOfArray([1,2,3,4]) );

Answer 1

 const input = [1,2,3,4] const theFunctionYouWannaWrite = (acc, v) => { acc.push(v + (acc[acc.length - 1] || 0)) return acc; } const output = input.reduce(theFunctionYouWannaWrite, []) console.log(output)

if you want to use it with for

 const input = [1,2,3,4] const theFunctionYouWannaWrite = (acc, v) => { acc.push(v + (acc[acc.length - 1] || 0)) return acc; } function sumOfArray(nums) { var output = []; for(let i = 0 ; i < nums.length ; i++) { theFunctionYouWannaWrite(output, nums[i]) } return output; }; console.log(sumOfArray(input))

Answer 2

Just add first item in array initialization and everything works fine.

 function sumOfArray(nums) { var output = [nums[0]]; // tip: initialize like let output = [nums?.[0] ?? 0]; for(let i = 1 ; i < nums.length ; i++) { nums[i] = nums[i] + nums[i-1]; output.push(nums[i]); } return output; }; console.log( 'calling sumOfArray([1,2,3,4])', sumOfArray([1,2,3,4]) );

Answer 3

 let sum = 0, nums = [1, 2, 3, 4], res = []; nums.forEach((item, index, arr) => { sum += arr[index]; res.push(sum); }); console.log(res);

Answer 4

You can do it using Array.prototype.reduce .

 function sumOfArray(nums) { return nums.reduce((s, n) => (s.push((s.at(-1) ?? 0) + n), s), []); } console.log(sumOfArray([1, 2, 3, 4]));

And the problem with your solution is that you need start the loop from index 0 and check if the i-1 th index is valid using either ?? or || .

 function sumOfArray(nums) { const output = []; for (let i = 0; i < nums.length; i++) { nums[i] = nums[i] + (nums[i - 1] ?? 0); output.push(nums[i]); } return output; } console.log(sumOfArray([1, 2, 3, 4]));

Other relevant documentations:

• Array.prototype.at
• Nullish coalescing operator (??)
• Comma operator (,)