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前言

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一、力扣647. 回文子串

class Solution {public int countSubstrings(String s) {int n = s.length();boolean[][] dp = new boolean[n][n];int res = 0;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){res ++;dp[i][j] = true;}else if(dp[i+1][j-1]){res ++;dp[i][j] = true;}}}}return res;}
}

class Solution {public int countSubstrings(String s) {int res = 0;for(int i = 0; i < s.length(); i ++){res += fun(i,i,s);res += fun(i,i+1,s);}return res;}public int fun(int start, int end, String s){int res = 0;while(start >= 0 && end < s.length()){if(s.charAt(start) != s.charAt(end)){return res;}start --;end ++;res ++;}return res;}
}

二、力扣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{dp[i][j] = Math.max(dp[i][j-1], dp[i+1][j]);}}}return dp[0][n-1];}  
}