【代码随想录训练营】【Day 60】【动态规划-13】| Leetcode 647, 516
需强化知识点
- 动态规划-回文系列
题目
647. 回文子串
- 注意sum（dp）不行
- j的遍历要倒序，并且 for j in range(i, n):
class Solution:def countSubstrings(self, s: str) -> int:n = len(s)dp = [[0]*(n) for _ in range(n)]result = 0for i in range(n-1, -1, -1):for j in range(i, n):if s[i] == s[j]:if j - i == 0:dp[i][j] = 1result += 1elif abs(j - i) == 1:dp[i][j] = 1result += 1else:dp[i][j] = dp[i+1][j-1]if dp[i+1][j-1]:result += 1else:dp[i][j] = 0return sum([sum(sublist) for sublist in dp])
516. 最长回文子序列
- 注意 python int max为 2**31 -1
- 滑动窗口，固定结束位置的方式，然后注意nums包含0，所以while判断是>=
class Solution:def longestPalindromeSubseq(self, s: str) -> int:n = len(s)# 以 i，j 的 最长序列长度dp = [[0] * (n) for _ in range(n)]for i in range(n):dp[i][i] = 1for i in range(n-1, -1, -1):for j in range(i+1, n):if s[i] == s[j]:dp[i][j] = dp[i+1][j-1] + 2else:dp[i][j] = max(dp[i+1][j], dp[i][j-1])return dp[0][n-1]
