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 n = s.size(), ans = 0;
        for (int i = 0; i < 2 * n - 1; ++i) {
            int l = i / 2, r = i / 2 + i % 2;
            while (l >= 0 && r < n && s[l] == s[r]) {
                --l;
                ++r;
                ++ans;
            }
        }
        return ans;
    }
};

516. 最长回文子序列

class Solution {
public:
    int longestPalindromeSubseq(string s) {
        int n = s.length();
        vector> dp(n, vector(n));
        for (int i = n - 1; i >= 0; i--) {
            dp[i][i] = 1;
            char c1 = s[i];
            for (int j = i + 1; j < n; j++) {
                char c2 = s[j];
                if (c1 == c2) {
                    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][n - 1];
    }
};