LeetCode练题——53. Maximum Subarray

1、题目

53. Maximum Subarray——Easy

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.

2、我的解法

(1)超时的暴力解法

 # -*- coding: utf-8 -*-
 # @Time    : 2020/2/6 22:15
 # @Author  : SmartCat0929
 # @Email   : 1027699719@qq.com
 # @Link    : https://github.com/SmartCat0929
 # @Site    :
 # @File    : 53. Maximum Subarray(超时的暴力算法）.py
 from typing import List

 class Solution:
     def maxSubArray(self, nums: List[int]) -> int:
         maxSum = -9999999999
         if len(nums)>1:
             maxSum = -99999
             for i in range(0, len(nums)):
                 for j in range(i, len(nums)):
                     thisSum = sum(nums[i:j+1])
                     if thisSum > maxSum:
                         maxSum = thisSum
             return maxSum
         elif len(nums)==1:
             maxSum=nums[0]
             return maxSum
         else:
             return 0

 print(Solution().maxSubArray([-2,1,-3,4,-1,2,1,-5,4]))

（2）局部最大值（copy大神）

 # -*- coding: utf-8 -*-
 # @Time    : 2020/2/7 16:12
 # @Author  : SmartCat0929
 # @Email   : 1027699719@qq.com
 # @Link    : https://github.com/SmartCat0929
 # @Site    :
 # @File    : 53. Maximum Subarray.py

 from typing import List
 class Solution:
     def maxSubArray(self, nums: List[int]) -> int:
         n = len(nums)
         tmp = 0
         res = float('-inf')
         for i in range(n):
             if tmp < 0:
                 tmp = 0
             tmp = tmp + nums[i]
             res = max(res, tmp)
         return res
 print(Solution().maxSubArray([-2,1,-3,4,-1,2,1,-5,4]))