You are given an array of integers (both positive and negative). Find the contiguous sequence with the largest sum. Return the sum.

Example:

Input:  [-2,1,-3,4,-1,2,1,-5,4]

Output:  6

Explanation:  [4,-1,2,1] has the largest sum 6.

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.