5最长回文子串

class Solution {
    public String longestPalindrome(String s) {
        if (s.length() == 0 || s == null) {
            return "";
        }
        int length = s.length();
        char[] str = s.toCharArray();
        boolean[][] dp = new boolean[length][length];
        for (int i = 0; i < length; i++) {
            dp[i][i] = true;
        }
        int max = 1;
        String maxStr = s.substring(0,1);
        for (int i = 1; i < length; ++i) {
            for (int j = 0; j + i < length; ++j) {
                if (str[j] == str[i + j]) {
                    if(j + 1 < i + j - 1 && !dp[j+1][i+j-1]){
                        dp[j][i+j] = false;
                    }else{
                        dp[j][i+j] = true;
                        max = Math.max(max,i + 1);
                        maxStr = s.substring(j,i+j+1);
                    }

                }
            }
        }

        return maxStr;
    }
}