LeetCode Maximum Subarray

LeetCode Maximum Subarray
Solving LeetCode with Maximum Subarray

Original question

Returns the largest child array in an array.

Note:

Negative values

Example:

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

Output: 6 (array [4,-1, 2, 1] and)

Solutions

It is also a classic question of dynamic planning. The following concepts are used to calculate the optimal subarray (and maximum) and dp [] at the end of the subarray using the k number, and then calculate the maximum value in dp. So what is the recursive relationship? When we put the next number num [k + 1] at the end of the number, it depends on whether the sum of the subarray connected to it is positive, if it is positive, add it; otherwise, discard it. The following code calculates the sum of dp and the maximum value in dp, so there is no additional array dp.

Another question is that the sub-array connected to num [k + 1] should be defined as multi-length, its starting position is the nearest and satisfying the sum of the subarrays connected to the number and the negative number. For example[-2, 1, -3, 4, -1, 2, 1, -5, 4]The beginning of the sub-array before-3 is 1,-1 is 4, and-5 is also 4.

AC Source Code

class Solution(object):    def maxSubArray(self, nums):        """        :type nums: List[int]        :rtype: int        """        if not nums:            return 0        length = len(nums)        current = nums[0]        m = current        for i in range(1, length):            if current < 0:                current = 0            current += nums[i]            m = max(current, m)        return mif __name__ == "__main__":    assert Solution().maxSubArray([-2, 1, -3, 4, -1, 2, 1, -5, 4]) == 6