代码随想录算法训练营第56天|● 647. 回文子串 ● 516.最长回文子序列

● 647. 回文子串

class Solution {
public:
    int countSubstrings(string s) {
        int res = 0;
        vector> dp(s.size(), vector(s.size(), false));
        for (int i = s.size() - 1; i >= 0; i--) {
            for (int j = i; j < s.size(); j++) {
                if (s[i] == s[j] && ((j - i <= 1) || dp[i + 1][j - 1])) {
                    res++;
                    dp[i][j] = true;
                }
            }
        }
        return res;
    }
};

● 516.最长回文子序列

class Solution {
public:
    int longestPalindromeSubseq(string s) {
        vector> dp(s.size(), vector(s.size(), 0));
        //int len = 1;
        for (int i = 0; i < s.size(); i++) {
            dp[i][i] = 1;
        }
        for (int i = s.size() - 1; i >= 0; i --) {
            for (int j = i + 1; j < s.size(); j ++) {
                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][s.size() - 1];
    }
};