03. Running Sum of 1d Array.cpp

/*
Running Sum of 1d Array
=======================

Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).

Return the running sum of nums.

Example 1:
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].

Example 2:
Input: nums = [1,1,1,1,1]
Output: [1,2,3,4,5]
Explanation: Running sum is obtained as follows: [1, 1+1, 1+1+1, 1+1+1+1, 1+1+1+1+1].

Example 3:
Input: nums = [3,1,2,10,1]
Output: [3,4,6,16,17]

Constraints:
1 <= nums.length <= 1000
-10^6 <= nums[i] <= 10^6

Hint #1  
Think about how we can calculate the i-th number in the running sum from the (i-1)-th number.
*/

class Solution
{
public:
  vector<int> runningSum(vector<int> &nums)
  {
    for (int i = 1; i < nums.size(); ++i)
    {
      nums[i] += nums[i - 1];
    }
    return nums;
  }
};