代码随想训练营第五十三天（Python）｜ 1143.最长公共子序列 、1035.不相交的线 、53. 最大子序和

1143.最长公共子序列

class Solution:
    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        m, n = len(text1), len(text2)
        # dp 数组代表 text1 以 i-1 结尾和 text2 以 j-1 结尾的最长公共子序列长度
        dp = [[0] * (m+1) for _ in range(n+1)]

        for i in range(1, n+1):
            for j in range(1, m+1):
                if text1[j-1] == text2[i-1]:
                    dp[i][j] = dp[i-1][j-1] + 1
                else:
                    dp[i][j] = max(dp[i-1][j], dp[i][j-1])

        return dp[n][m]

1035.不相交的线

class Solution:
    def maxUncrossedLines(self, nums1: List[int], nums2: List[int]) -> int:
        m, n = len(nums1), len(nums2)
        dp = [[0] * (m+1) for _ in range(n+1)]

        for i in range(1, n+1):
            for j in range(1, m+1):
                if nums1[j-1] == nums2[i-1]:
                    dp[i][j] = dp[i-1][j-1] + 1
                else:
                    dp[i][j] = max(dp[i-1][j], dp[i][j-1])

        return dp[n][m]

53. 最大子序和
1、动态规划

class Solution:
    def maxSubArray(self, nums: List[int]) -> int:
        # dp 代表 nums[i] 结尾时的最大子数组和为 dp[i]
        dp = [0] * len(nums)

        dp[0] = nums[0]

        res = dp[0]

        for i in range(1, len(nums)):
            dp[i] = max(dp[i-1] + nums[i], nums[i])

            res = max(dp[i], res)

        return res

2、贪心
注意点: 先比较大小，再判断和是否小于 0

class Solution:
    def maxSubArray(self, nums: List[int]) -> int:
        sum1 = 0
        res = float('-inf')
        for num in nums:
            sum1 += num
            res = max(res, sum1)
            if sum1 < 0:
                sum1 = 0
        return res