Problem 4 - Project Euler in Java by Jane Ullah

Problem4.java

/**
 * 
 * @author Jane Ullah
 * @date   12/19/2011
 * @purpose Solving Problem 4 from ProjectEuler.net
 *
 */
public static void main(String[] args) {
	/*if (isPalindrome(1222321))	{
		System.out.println("Yes.");
	}*/
	boolean loopControl = false;
	String palindrome = "";
	for (int i = 1000000; !loopControl; i--)	{
		if (isPalindrome(i))	{
			palindrome = valid3DigitDivisor(i);
			if ( !(palindrome == "")) {
				System.out.println("largest palindrome is: " + i);
				loopControl = true;
			}
		}
	}
	
}

//Method to test for palindromes; Separated out for ease of reading.
private static boolean isPalindrome(int number){
        //converting the number to a String
	String dummy = "" + number;
	int index;
        //Compares the ends of the String and terminates when a single mismatch is found
	for (index = 1; index <= dummy.length()/2 && ( (dummy.charAt((dummy.length()-index)) == dummy.charAt((index-1)) ) ); index++);
	return (index > dummy.length()/2);
}

//Method to check the palindrome's factors and select those that are 3 digit numbers
//Returns an empty string if no 3 digit numbers (whose product is the palindrome) were found.
private static String valid3DigitDivisor(int palindrome){
	int j, loopControl = (int) Math.floor(Math.sqrt(palindrome));
	String divisor, quotient, result = "";
	for (j = 0; j <= loopControl; j++)	{
                //Catching divisors of the palindrome
		if ( (palindrome % (j+2) == 0) )	{
			divisor = "" + (j+2);
			quotient = "" + (palindrome/(j+2));
                        //Selecting for numbers (divisor and quotient) that are 3 digits
			if ( (divisor.length() == 3) && (quotient.length() == 3) )	{
				result =  divisor + " " + quotient;
			}	
		}
	}
	return result;