Given an integer array `nums`, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

A subarray is a contiguous part of an array.

Example 1:

    Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
    Output: 6
    Explanation: [4,-1,2,1] has the largest sum = 6.

Example 2:

    Input: nums = [1]
    Output: 1

Example 3:

    Input: nums = [5,4,-1,7,8]
    Output: 23

Constraints:

- `1 <= nums.length <= 105`
- `-104 <= nums[i] <= 104`

Follow up: If you have figured out the `O(n)` solution, try coding another solution using the divide and conquer approach, which is more subtle.