/* 
 * RecurPalindrome - implementing a recursive method for determining 
 * if a string is a palindrome
 */

import java.util.Scanner;

public class RecurPalindrome {
    public static void main(String[] args) {
        System.out.println("\nWelcome to the Palindrome Test Program!");

        // Reads in one string from the user
        Scanner userInput = new Scanner(System.in);
        System.out.print("\nType in a word and press enter: ");
        String word = userInput.next();
        userInput.close();

        // Call the recursive function here by replacing true with your call.
        boolean isPalindrome = rPalindrome(word);

        // Printing out the result
        if (isPalindrome) {
            System.out.println("Palindrome!");
        } else {
            System.out.println("Not a palindrome!");
        }
    }

    private static boolean rPalindrome(String s) {
        int length = s.length();
        
        // first base case: s is empty or has only one character
        if (length <= 1) {
            return true;
        } 

        // second base case: outer characters don't match
        if (s.charAt(0) != s.charAt(length-1)) {
            return false;
        }

        // recursive case
        return rPalindrome(s.substring(1, length-1));
    }

    // alternative solution with a single return statement and 
    // an implicit base case
    private static boolean rPalindrome2(String s) {
        boolean isPal = true;

        if (s.length() > 1) {
            int length = s.length();
            if (s.charAt(0) == s.charAt(length-1)) {
                isPal = rPalindrome2(s.substring(1, length-1));
            } else {
                isPal = false;
            }
        }

        return isPal;
    }
}