53. Maximum Subarray

https://leetcode.com/problems/maximum-subarray/description/

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

问和最大的子数组的和是多少。max + subarray => DP/窗口。 dp[i]为以i为结尾的最长连续子数组的长度，action为是单独形成一个新subarray还是和前面的拼一起，取决于上一个最优是否为负。

class Solution:
    def maxSubArray(self, nums: List[int]) -> int:
        dp, res = 0, float('-inf')
        for _, v in enumerate(nums):
            dp = max(dp, 0) + v
            res = max(dp, res)
        return res