C++

1/*
2 * Runtime: 12 ms, faster than 13.10% 
3 * Memory Usage: 8.9 MB, less than 98.70%
4 */
5class Solution {
6public:
7    vector<int> runningSum(vector<int>& nums) {
8        vector<int> result;
9        for(int i=0; i<nums.size(); ++i)
10        {
11            int sum = 0;
12            for(int j=0; j<i+1; ++j)
13            {
14                sum += nums[j];
15            }
16            result.push_back(sum);
17        }
18        return result;
19    }
20};
21
22/*
23 * Runtime: 4 ms, faster than 84.50% 
24 * Memory Usage: 8.9 MB, less than 98.70%
25*/
26class Solution {
27public:
28    vector<int> runningSum(vector<int>& nums) {
29        int sum = 0;
30        for(int i=0; i<nums.size(); ++i)
31        {
32            sum += nums[i];
33        }
34        
35        int neg = nums[nums.size()-1];
36        nums[nums.size()-1] = sum;
37        for (int i=nums.size()-2; i>=0; --i)
38        {
39            int val = sum-neg;
40            neg += nums[i];
41            nums[i] = val;
42        }
43        return nums;
44    }
45};

JavaScript

1/**
2 * Runtime: 80 ms, faster than 66.97%
3 * Memory Usage: 38.7 MB, less than 5.17%
4 */
5var runningSum = function(nums) {
6    let sum = nums.reduce((a, b) => a + b, 0);
7    let neg = nums[nums.length-1];
8    nums[nums.length-1] = sum;
9    
10    for (let i=nums.length-2; i>=0; --i) {
11        let val = sum - neg;
12        neg += nums[i];
13        nums[i] = val;
14    }
15    
16    return nums;
17};

Ruby

1=begin
2 Runtime: 52 ms, faster than 72.86% 
3 Memory Usage: 210.1 MB, less than 81.12%
4=end
5def running_sum(nums)
6    sum = nums.sum
7    nums << sum;
8    
9    (nums.size-2).downto(0) do |i|
10        temp = nums[i]
11        nums[i] = sum - nums[i];
12        sum -= temp
13    end
14    
15    nums.shift
16    nums
17end