代码随想录算法训练营第五十七日| ● 647. 回文子串 ● 516.最长回文子序列

647. 回文子串：

class Solution:
    def countSubstrings(self, s: str) -> int:
        dp = [[False] * len(s) for _ in range(len(s))]
        result = 0
        for i in range(len(s)-1, -1, -1): #注意遍历顺序
            for j in range(i, len(s)):
                if s[i] == s[j] and (j - i <= 1 or dp[i+1][j-1]): 
                    result += 1
                    dp[i][j] = True
        return result

516.最长回文子序列

class Solution:
    def longestPalindromeSubseq(self, s: str) -> int:
        dp = [[0] * len(s) for _ in range(len(s))]
        for i in range(len(s)):
            dp[i][i] = 1
        for i in range(len(s)-1, -1, -1):
            for j in range(i+1, len(s)):
                if s[i] == s[j]:
                    dp[i][j] = dp[i+1][j-1] + 2
                else:
                    dp[i][j] = max(dp[i+1][j], dp[i][j-1])
        return dp[0][-1]