【LeetCode每天一题】Maximum Subarray(最大子数组)

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.

思路

　　第二种思路就是我们设置一个sum_标志量和结果变量，然后从头遍历，使用sum_变量存储连续数组的和，如果当前小于0直接赋值为0。最后返回结果变量。时间复杂度为O(n)，空间复杂度为O(1)。

第一种思路代码

 1 class Solution(object):
 2     def maxSubArray(self, nums):
 3         """
 4         :type nums: List[int]
 5         :rtype: int
 6         """
 7         if len(nums) < 1 :
 8             return  0
 9         dp = [0] * len(nums)     # 辅助数组
10         dp[0] = nums[0]    # 记录nums第一个的值
11         max_num = dp[0]     # 记录子数组最大的值
12         for i in range(1, len(nums)):
13             dp[i] = nums[i] + (dp[i-1] if dp[i-1]> 0 else 0)   # 记录当前最大的子数组和的值
14             max_num = max(max_num, dp[i])
15         return max_num

第二种思路解决办法

 1 class Solution(object):
 2     def maxSubArray(self, nums):
 3         """
 4         :type nums: List[int]
 5         :rtype: int
 6         """
 7         if len(nums) < 1 :
 8             return  0
 9         res, sum_ = nums[0], 0
10         for i in nums:
11             sum_ += i
12             res = max(sum_, res)
13             if sum_ < 0:
14                 sum_ = 0
15         return res

原文地址：https://www.cnblogs.com/GoodRnne/p/10726043.html