leetcode(5)最长回文子串

class Solution {
    public String longestPalindrome(String s) {
        int len = s.length();
        boolean[][] b = new boolean[len][len];
        int max = 0;
        int begin = 0;
        for(int i=0;i<len;i++){
            for(int j=0;j<=i;j++){
                if(s.charAt(i)==s.charAt(j)&&(i-j<=2 || b[j+1][i-1])){
                    b[j][i] = true;
                    if(i-j+1>max){
                        max = i - j + 1;
                        begin = j;
                    }
                }
            }
        }
        return s.substring(begin,begin+max);
    }
}