Given an integer array `nums`, find the subarray with the largest sum, and return its sum.
**Example 1:**
```
Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
Output: 6
Explanation: The subarray [4,-1,2,1] has the largest sum 6.
```
**Example 2:**
```
Input: nums = [5,4,-1,7,8]
Output: 23
```