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LeetCode53_最大子序和


1. 题目

给定一个整数数组 nums ,找到一个具有最大和的连续子数组(子数组最少包含一个元素),返回其最大和。

示例 1
输入:nums = [-2,1,-3,4,-1,2,1,-5,4]
输出:6
解释:连续子数组 [4,-1,2,1] 的和最大,为 6

示例 2
输入:nums = [1]
输出:1

示例 3
输入:nums = [0]
输出:0

示例 4
输入:nums = [-1]
输出:-1

示例 5
输入:nums = [-100000]
输出:-100000

提示:
1 <= nums.length <= 105
-104 <= nums[i] <= 104

进阶:如果你已经实现复杂度为 O(n)

2. 题解

import math
from typing import List


class Solution:
# 直接超时了,不行
def maxSubArray(self, nums: List[int]) -> int:
n = len(nums)
if n == 0:
return 0
max_sum = float('-inf')
for i in range(n):
total = 0
for j in range(i, n):
total += nums[j]
max_sum = max(total, max_sum)
return max_sum

# 前缀和
def maxSubArray_1(self, nums: List[int]) -> int:
n = len(nums)
if n == 0:
return 0
max_s = nums[0]
min_s = 0
total = 0
for m in nums:
total += m
max_s = max(max_s, total - min_s)
min_s = min(total, min_s)
return max_s

# 动态规划
def maxSubArray_2(self, nums: List[int]) -> int:
n = len(nums)
max_cur = nums[0]
max_sum = nums[0]
for i in range(1, n):
max_cur = max(max_cur + nums[i], nums[i])
max_sum = max(max_cur, max_sum)
return max_sum


if __name__ == "__main__":
s = Solution()
nums = [1]
a = s.maxSubArray_1(nums)
print(a)


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