Find the longest palindromic substring

LeetCodeTwo

package com.westudio.java;

public class LeetCodeTwo {

    public static void main(String[] argv) {
    }

    /**
     * Naive programing
     * @param s
     * @return
     */
    public static String longestPalindromeOne(String s) {
        int longest = 0;
        int length = s.length();
        String longestPalindrome = null;

        for (int i = 0; i < length; i++) {
            for (int j = i + 1; j < length; j++) {
                int len = j - i;
                String str = s.substring(i, j + 1);
                if (isPalindrome(str)) {
                    if (len > longest) {
                        longest = len;
                        longestPalindrome = str;
                    }
                }
            }
        }

        return longestPalindrome;
    }

    /**
     * Dynamic programming
     * @param s
     * @return the longest palindrome string
     */
    public static String longestPalindromeTwo(String s) {
        if (s == null)
            return null;

        if (s.length() <= 1)
            return s;

        int longest = 0;
        String longestPalindrome = null;

        int length = s.length();
        int[][] table = new int[length][length];

        // every single letter is palindrome
        for (int i = 0; i < length; i++) {
            table[i][i] = 1;
        }
        longest = 1;
        printTable(table);

        // two consecutive same letters are palindrome
        for (int i = 0; i <= length - 2; i++) {
            if (s.charAt(i) == s.charAt(i + 1)) {
                table[i][i+1] = 1;
                longestPalindrome = s.substring(i, i + 2);
                longest = 2;
            }
        }
        printTable(table);

        for (int l = 3; l <= length; l++ ) {
            for (int i = 0; i <= length - l; i++) {
                int j = i + l - 1;
                if (s.charAt(i) == s.charAt(j)) {
                    table[i][j] = table[i+1][j-1];
                    if (table[i][j] == 1 && l > longest) {
                        longestPalindrome = s.substring(i, j + 1);
                    }
                } else {
                    table[i][j] = 0;
                }
                printTable(table);
            }
        }
        return longestPalindrome;
    }

    /**
     * Simplest way
     * @param s
     * @return
     */
    public static String longestPalindromeThree(String s) {
        if (s.isEmpty()) {
            return null;
        }
        if (s.length() == 1) {
            return s;
        }

        String longest =s.substring(0, 1);
        for (int i = 0; i < s.length(); i++) {
            String temp = center(s, i, i);
            if (temp.length() > longest.length()) {
                longest = temp;
            }

            temp = center(s, i, i + 1);
            if (temp.length() > longest.length()) {
                longest = temp;
            }
        }
        return longest;
    }

    public static boolean isPalindrome(String s) {

        for (int i = 0; i < s.length() - 1; i++) {
            if (s.charAt(i) != s.charAt(s.length() - 1 - i)) {
                return false;
            }
        }

        return true;
    }

    public static void printTable(int[][] table) {
        for (int[] y : table) {
            for (int z : y) {
                System.out.print(z + " ");
            }
            System.out.println();
        }
        System.out.println("-------");
    }

    public static String center(String s, int begin, int end) {
        while (begin >= 0 && end <= s.length() - 1 && s.charAt(begin) == s.charAt(end)) {
            begin --;
            end ++;
        }
        return s.substring(begin + 1, end);
    }
}