package strings;

/**
 * Wikipedia: https://en.wikipedia.org/wiki/Palindrome
 */
class Palindrome {

 /**
 * Driver Code
 */
 public static void main(String[] args) {
 String[] palindromes = {null, "", "aba", "123321"};
 for (String s : palindromes) {
 assert isPalindrome(s) && isPalindromeRecursion(s) && isPalindrome1(s);
 }

 String[] notPalindromes = {"abb", "abc", "abc123"};
 for (String s : notPalindromes) {
 assert !isPalindrome(s) && !isPalindromeRecursion(s) && !isPalindrome1(s);
 }
 }

 /**
 * Check if a string is palindrome string or not
 *
 * @param s a string to check
 * @return {@code true} if given string is palindrome, otherwise {@code false}
 */
 public static boolean isPalindrome(String s) {
 return (s == null || s.length() <= 1) || s.equals(new StringBuilder(s).reverse().toString());
 }

 /**
 * Check if a string is palindrome string or not using recursion
 *
 * @param s a string to check
 * @return {@code true} if given string is palindrome, otherwise {@code false}
 */
 public static boolean isPalindromeRecursion(String s) {
 if (s == null || s.length() <= 1) {
 return true;
 }

 if (s.charAt(0) != s.charAt(s.length() - 1)) {
 return false;
 }

 return isPalindrome(s.substring(1, s.length() - 1));
 }

 /**
 * Check if a string is palindrome string or not another way
 *
 * @param s a string to check
 * @return {@code true} if given string is palindrome, otherwise {@code false}
 */
 public static boolean isPalindrome1(String s) {
 if (s == null || s.length() <= 1) {
 return true;
 }
 for (int i = 0, j = s.length() - 1; i < j; ++i, --j) {
 if (s.charAt(i) != s.charAt(j)) {
 return false;
 }
 }
 return true;
 }
}