代码随想录训练营day46|动态规划part13

回文子串

力扣题目链接

class Solution {
public:
    //判断是否是回文
    bool isHuiwen(string &s, int i, int j){
        while(i <= j){
            if(s[i] != s[j])
                return false;
            i++;
            j--;
        }
        return true;
    }

    int countSubstrings(string s) {
        int len = s.length();
        vector<vector<int>> dp(len, vector<int>(len, 0));
        // dp[j][j+i]:  j -> j+i
        for(int i = 0; i < len; i++){
            for(int j = 0; j+i < len; j++){
                if(i == 0){
                    dp[j][j+i] = 1;
                }
                else if(i == 1){
                    dp[j][j+i] = dp[j][j+i-1] + dp[j+1][j+i];
                    if(s[j] == s[j+i])
                        dp[j][j+i]++;
                }
                else{
                    dp[j][j+i] = dp[j][j+i-1] + dp[j+1][j+i] - dp[j+1][j+i-1];
                    if(s[j] == s[j+i] && isHuiwen(s, j, j+i))
                        dp[j][j+i]++;
                }
            }
        }
        return dp[0][len-1];
    }
};

最长回文子序列

力扣题目链接

class Solution {
public:
    int longestPalindromeSubseq(string s) {
        int len = s.length();
        vector<vector<int>> dp(len, vector<int>(len, 1));
        for(int i = 1; i < len; i++){
            for(int j = 0; i+j < len; j++){
                if(i == 1){
                    if(s[j] == s[i+j]){
                        dp[j][i+j] = 2;
                    }
                }
                else{
                    if(s[j] == s[i+j]){
                        dp[j][j+i] = max(dp[j+1][j+i-1] + 2, max(dp[j+1][j+i], dp[j][j+i-1]));
                    }
                    else{
                        dp[j][j+i] = max(dp[j+1][j+i], dp[j][j+i-1]);
                    }
                }
            }
        }
        return dp[0][len-1];
    }
};