Find the contiguous subarray within an array (containing at least one number) which has the largest sum.

For example, given the array[-2,1,-3,4,-1,2,1,-5,4],
the contiguous subarray[4,-1,2,1]has the largest sum =6.

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

import sys
class Solution(object):
    def maxSubArray(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if nums == []:
            return 0
        elif len(nums) == 1:
            return nums[0]
        elif len(nums) == 2:
            return max(nums[0], nums[1], nums[0]+nums[1])
        else:
            all_neg = True
            for entries in nums:
                if entries >= 0:
                    all_neg = False
            if all_neg == False:
                curr_sum = 0
                max_sum = - sys.maxsize - 1
                for i in range(len(nums)):
                    curr_sum += nums[i]
                    if curr_sum < 0:
                        curr_sum = 0
                    if curr_sum > max_sum:
                        max_sum = curr_sum
                return max_sum
            else:
                return max(nums)