5_longest_palindromic_substring.java

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

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

        for (int right = 1; right < length; right++) {
            for (int left= 0; left < right; left++) {
                
                if (s.charAt(left) != s.charAt(right)) {
                    dp[left][right] = false;
                } else {
                    if (right - left < 3) {
                        dp[left][right] = true;
                    } else {
                        dp[left][right] = dp[left+1][right-1];
                    }
                }

                if (dp[left][right] == true && (right - left + 1 > maxLength)) {
                    maxLength = right - left + 1;
                    begin = left;
                }
            }
        }

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

/**
 * This is my personal record of solving Leetcode Problems. 
 * If you have any questions, please discuss them in [Issues](https://github.com/mengxinayan/leetcode/issues).
 * Copyright (C) 2020-2022  mengxinayan
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */