【代码随想录Day57 动态规划 part17】647.回文子串、516.最长回文子序列

Day57

647.回文子串

class Solution {
   public int countSubstrings(String s) {
        int n = s.length();
        int res = 0;
        boolean dp[][] = new boolean[n][n];
        for (int i = n - 1; i >= 0; i--) {
            for (int j = i; j < n; j++) {
                if(s.charAt(i) == s.charAt(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) {
        int n = s.length();
        int dp[][] = new int[n][n];
        for (int i = n - 1; i >= 0; i--) {
            for (int j = i; j < n; j++) {
                if (s.charAt(i) == s.charAt(j)) {
                    if (j - i <= 1) dp[i][j] = j - i + 1;
                    else dp[i][j] = dp[i + 1][j - 1] + 2;
                } else {
                    if (j - i <= 1) dp[i][j] = 1;
                    else dp[i][j] = Math.max(dp[i + 1][j],dp[i][j - 1]);
                }
            }
        }
        return dp[0][n - 1];
    }
}