/*
 * Projlet6_palindromes.java
 *
 * Created on August 17, 2003, 9:53 PM
 */

/** Projlet #6 programming solution for palindrome problems
 */
public class Projlet6_palindromes {
    
    /*************************** 2a ******************************/
    /** See if the string is an exact palindrome.  Case and non-letter
     *  characters must match exactly.
     */
    public static boolean isExactPalindrome(String message) {
        if (message == null) { 
            return false;
        }
        if (message.length() <= 0) { //these are real base cases
            return true;
        }
        return isExactPalindrome(message, 0,  message.length()-1);        
    }
    
    /** Check whether the portion of the string between indices lo and hi 
     * (inclusive) is an exact palindrome.
     * Preconditions: message is not null.  lo and hi are in bounds.
     */
    private static boolean isExactPalindrome(String message, int lo, int hi) {
        assert lo >= 0 && hi >= lo && hi < message.length(): lo + " " + hi;
        if (lo == hi) {  //base case -- a string of length 1
            return true;
        }
        if (message.charAt(lo) != message.charAt(hi)) {
            //base case -- the outer characters don't match
            return false;
        }
        if (hi == lo+1) {
            return true; //base case -- two-letter string of duplicate chars.
        }
        return isExactPalindrome(message, lo+1, hi-1);
    }

    /************************ 2b **********************************************/
    /** See if the string is a palindrome, disregarding case and ignoring
       all non-letter characters.
     */
    public static boolean isPalindrome(String message) {
        if (message == null) { 
            return false;
        }
        if (message.length() <= 1) { //these are real base cases
            return true;
        }
        return isPalindrome(message, 0,  message.length()-1);        
    }
    
    /** Check whether the portion of the string between indices lo and hi 
     * (inclusive) is a (general) palindrome.
     * Preconditions: message is not null.  lo and hi are in bounds.
     */
    private static boolean isPalindrome(String message, int lo, int hi) {
        assert lo >= 0 && hi >= lo && hi < message.length(): lo + " " + hi;
        if (lo == hi) {  //base case -- a string of length 1
            return true;
        }
        char loChar = message.charAt(lo);
        if (!Character.isLetter(loChar)) {
            return isPalindrome(message, lo+1,  hi);//skip non-letter character
        }
        char hiChar = message.charAt(hi);
        if (!Character.isLetter(hiChar)) {
            return isPalindrome(message, lo, hi-1);//skip non-letter character
        }
        //we now are sure there are two letter characters to be compared
        if (Character.toLowerCase(loChar) != Character.toLowerCase(hiChar)) {
            //base case -- the outer characters don't match
            return false;
        }
        //The outer chars are the same (except perhaps for case)
        if (hi == lo+1) {
            return true; //base case -- two-letter string of duplicate chars.
        }
        return isPalindrome(message, lo+1, hi-1);
    }
    
    /**  For testing.
     * @param args the command line arguments (ignored).
     */
    public static void main(String[] args) {
        assert isExactPalindrome("");
        assert !isExactPalindrome(null);
        assert isExactPalindrome("X");
        assert isExactPalindrome("aa");
        assert !isExactPalindrome("Aa");
        assert isExactPalindrome("ABA");
        assert isExactPalindrome("ABBA");
        assert isExactPalindrome("AB BA");
        assert !isExactPalindrome("AB CBA");
        assert !isExactPalindrome(" ABBA");


        assert isPalindrome("");
        assert !isPalindrome(null);
        assert isPalindrome("X");
        assert isPalindrome("aa");
        assert isPalindrome("Aa");
        assert isPalindrome("ABA");
        assert isPalindrome("ABBA");
        assert isPalindrome("AB BA");
        assert isPalindrome("AB CBA");
        assert isPalindrome(" ABBA");
        assert isPalindrome("Madam, I'm Adam!");
        assert !isExactPalindrome("Madam, I'm Adam!");
        assert !isPalindrome("Madame, I'm Adam.");
        assert !isPalindrome("Madam, I am Adam.");
        assert isPalindrome("          ,,..,,..a!!");
        assert isPalindrome("     a[]{}     ,,..,,..a!!");
        assert isPalindrome("     aa[]{} 1234567890!@#$%^&*()    ,,..,,..a!!");

        System.out.println("End palindromes test.");
    }
    
}