# Running Sum of 1d Array

{% embed url="<https://leetcode.com/problems/running-sum-of-1d-array/>" %}

## Solution 1 (Java)

```java
class Solution {
    public int[] runningSum(int[] nums) {
        int[] ans = new int[nums.length];
        ans[0] = nums[0];
        for (int i = 1; i < nums.length; i++) {
            ans[i] = ans[i - 1] + nums[i];
        }
        return ans;
    }
}
```

A little teaser for DP.

## Solution 2 (Java)

```java
class Solution {
    public int[] runningSum(int[] nums) {
        for (int i = 1; i < nums.length; i++) {
            nums[i] += nums[i - 1]; 
        }
        return nums;
    }
}
```

The separate array is not actually needed. We can do the adding process in place. The complexities stay the same though.

* Time complexity: `O(n)`
* Space complexity: `O(1)`