Total sum of an Array

Question

I'm working on a problem that requires the running sum within the array. Example, an array with the values [1,2,3,4] should return [1,3,6,10] and an array that holds [3,1,2,10,1] should output [3,4,6,16,17]. Right now I am stumped on what I am missing for my answer. I am thinking that I should handle this recursively in some way, but I am not sure how to begin with that. In any case, this is my current solution

var runningSum = function(nums) { let result = []; nums.forEach(function(num, idx) { if (idx === 0) { result.push(num); } else { result.push(num + nums[idx - 1]); } }); return result; }

Leet code stated that this was a fairly easy problem, so I figured that I'm thinking way too hard on this and can solve it a lot easier. Let me know your thoughts. Thanks!

change num + nums[idx - 1] to num + result[idx - 1] so that you actually take into the account the sum of previous numbers and not just the last number — Krzysztof Krzeszewski
– Krzysztof Krzeszewski, Commented Aug 9, 2022 at 9:14
Ah got it! Would it make sense to say that during the iteration, the nums array is represented by only one element? — jo A
– jo A, Commented Aug 9, 2022 at 9:18
You made it too complex: function runningSum(nums) { let temp = 0; return nums.map(el => (temp += el, temp)); } Example: wandbox.org/permlink/iOJnh6FR1cCBSu6z — user16540390
– user16540390, Commented Aug 9, 2022 at 9:22
@jabaa This works fine but writing to an external variable with .map() feels kind of icky to me ;) — user5734311
– user5734311, Commented Aug 9, 2022 at 9:25

jay · Accepted Answer · 2022-08-09 09:39:53Z

1

A simpler (and more resource-friendly) way of approaching the problem would just be to use a for loop:

/** * @param {number[]} nums * @return {number[]} */ var runningSum = function(nums) { for (let i = 1; i < nums.length; i++) nums[i] += nums[i-1]; return nums; };

answered Aug 9, 2022 at 9:39

jay

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3 Comments

jo A Over a year ago

Thank for you the response! When you say more resource-friendly, are you referring to space & time complexity? I am starting to learn more on this topic.

user16540390 Over a year ago

This modifes the input array. That's usually bad practice in JavaScript.

jay Over a year ago

I was referring to performance tests done by others shown here. Other methods (such as for, for...of) perform relatively better than .forEach().

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