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.

Solution

import sys
from typing import List

class Solution:
    def maxSubArray(self, nums: List[int]) -> int:
        maxSum = -sys.maxsize-1
        curSum = -sys.maxsize-1

        for i in range(len(nums)):
            curSum = max(nums[i], curSum + nums[i])
            maxSum = max(curSum, maxSum)

        return maxSum

Test Cases

test = Solution()
answer = test.maxSubArray([-2,1,-3,4,-1,2,1,-5,4])
assert answer == 6
answer = test.maxSubArray([-2])
assert answer == -2
answer = test.maxSubArray([-2,-3])
assert answer == -2
print('All Passed!')

Big O Analysis

Space Complexity: O(1)

Time Complexity: O(N)