LongestPalindromicSubstring.java

package DynamicProgramming;

/*
 * Algorithm explanation https://leetcode.com/problems/longest-palindromic-substring/
 */
public class LongestPalindromicSubstring {
	public static void main(String[] args) {
		String a = "babad";
		String b = "cbbd";

		String aLPS = LPS(a);
		String bLPS = LPS(b);

		System.out.println(a + " => " + aLPS);
		System.out.println(b + " => " + bLPS);
	}

	private static String LPS(String input) {
		if(input == null || input.length() == 0){
			return input;
		}
		boolean arr[][] = new boolean[input.length()][input.length()];
		int start = 0, end = 0;
		for (int g = 0; g < input.length(); g++) {
			for (int i = 0, j = g; j < input.length(); i++, j++) {

				if (g == 0) {
					arr[i][j] = true;
				} else if (g == 1) {
					if (input.charAt(i) == input.charAt(j)) {
						arr[i][j] = true;
					} else {
						arr[i][j] = false;
					}
				} else {

					if (input.charAt(i) == input.charAt(j) && arr[i + 1][j - 1]) {
						arr[i][j] = true;
					} else {
						arr[i][j] = false;
					}
				}

				if (arr[i][j]) {
					start = i;
					end = j;
				}
			}
		}
		return input.substring(start, end + 1);
	}

}