算法训练营day46(12.14)

题目1： 647. 回文子串
代码：

class Solution {
public:
    int countSubstrings(string s) {
        int n = s.length();
        vector<vector<bool>> dp(n, vector<bool>(n));

        int total = 0;
        for(int i = 0; i < n; i++) {
            dp[i][i] = true;
            total++;
        }

        for(int len = 2; len <= n; len++) {
            for(int i = 0; i + len <= n; i++) {
                int j = i + len - 1;
                if(s[i] != s[j]) {
                    continue;
                }
                if(len > 2 && !dp[i + 1][j - 1]){
                    continue;
                }
                dp[i][j] = true;
                ++total;
            }
        }
        return total;
    }
};

题目2： 516. 最长回文子序列

代码：

class Solution {
public:
    int longestPalindromeSubseq(string s) {
        int n = s.length();
        vector<vector<int>> dp(n, vector<int>(n));

        for(int i = 0; i < n; i++) dp[i][i] = 1;
        for(int i = n - 1; i >= 0; i--) {
            for(int j = i + 1; j < n; j++) {
                if(s[i] == s[j]) dp[i][j] = dp[i + 1][j - 1] + 2;
                else dp[i][j] = max(dp[i][j - 1], dp[i + 1][j]);
            }
        }
        return dp[0][n - 1];
    }
};