```
class Solution(object):
def maxSubArray(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
ret=-9999
prevsum=nums[0]
for i in range(1,len(nums)):
prevsum=max(nums[i],nums[i]+prevsum)
ret=max(ret,prevsum)
ret=max(nums[0],ret)
return ret
```

Every time to calculate the max sum starting from 0 end with n, we either take sum(nums[0:n-1])+nums[n] or nums[n], whichever is larger. In other words, if sum(nums[0:n-1)] is less than 0, than we will drop the nums[0:n-1].