// Check for palindromes ignoring non-alphanumeric.
// Book does it using StringBuilder
// This is the "equivalent" String-only soln.
// The real difference is my append vs Stringbuilder's append
// I use string concatination, which involves copying so is less efficient
import java.util.Scanner;
public class PalindromeOnlyAlpha {
    public static void main (String[] args) {
	Scanner getInput = new  Scanner(System.in);
	System.out.print("Enter a string: ");
	String s = getInput.nextLine();
	System.out.printf("%s\nis %s a palindrome? %s\n",
			  "Ignoring nonalpnumeric characters,",
			  s, isPalindrome(s));
    }

    public static boolean isPalindrome(String s) {
	String s1 = filter(s);
	String s2 = reverse(s1);
	return s2.equals(s1);
    }

    public static String filter(String s) {
	String answer = new String();
	for (int i=0; i<s.length(); i++)
	    if (Character.isLetterOrDigit(s.charAt(i)))
		answer = append(answer, s.charAt(i));
	return answer;
    }

    public static String reverse(String s) {
	String answer = new String();
	for (int i=0; i<s.length(); i++)
	    answer = append(answer, s.charAt(s.length()-1-i));
	return answer;
    }

    public static String append(String s, char c) {
	return s.concat(Character.toString(c));
    }
}