leetcode5. 最长回文子串(java)

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java：

class Solution {
    public String longestPalindrome(String s) {
        int len = s.length();
        if(len < 2){
            return s;
        }

        int maxlen = 1;
        int begin = 0;
        boolean[][] dp = new boolean[len][len];
        for(int i = 0; i < len; i++){
            dp[i][i] = true;
        }

        char[] ca = s.toCharArray();
        for(int L = 2; L <= len; L++){
            for(int i = 0; i < len; i++){
                int j = L + i - 1;
                if(j >= len){
                    break;
                }
                if(ca[i] != ca[j]){
                    dp[i][j] = false;
                }else{
                    if(j - i < 3){
                        dp[i][j] = true;
                    }else{
                        dp[i][j] = dp[i + 1][j - 1];
                    }
                }
            if(dp[i][j] && j - i + 1 > maxlen){
                maxlen = j - i + 1;
                begin = i;

                }
            }
        }
        return s.substring(begin, begin + maxlen);
    }
}