// THIS CODE IS MY OWN WORK, IT WAS WRITTEN WITHOUT CONSULTING
// A TUTOR OR CODE WRITTEN BY OTHER STUDENTS - YOUR NAME

/**
 * Euclid3 is a revision of Euclid.java from the start of the semester
 *
 * We compute the GCD (greatest common divisor) of two integers 
 * by the Euclid's algorithm, but now in a separate gcd method
 * that RETURNS the Greatest Common Divisor (instead of priniting it), 
 * which we will test several times from the main method.
 *
 * @version cs170 Fall 2011
 */

// TODO (in BlueJ):
//
//  * Remember to fix the honor statement.  (We interpret "THIS CODE"
//    to just mean the changes you make to this file.)
//
//  * Read what the main() method (see below) is doing
//
//  * Read what the testGcd() method (see below) is doing
//
//  * Read what the gcd() method (see below) is doing
//
//  * Compile and run the program in BlueJ.
//
//    You should see as the last line:
//        Passed 6 tests out of 7
//    This test fail:
//        Calling gcd(7, 0) ... GCD = 0 not 7, ERROR!
//
//  * Modify the gcd method so that it passes all the tests.
//    ONLY modify the method named "gcd" (the first one).
//    DO NOT modify the other two methods (main or testGcd).
//
//    Hint:
//       Right now, the "gcd" method always returns the variable B.
//       When one of the number is 0, the GCD is equal to the other number.
//       You must change:
//
//          return B;
//
//       to return a number based on some condition.
//       Use:
//          if ( A == 0 ) 
//             return ???
//          else
//             return ???
//
//    NOTE: Complete this task before moving on to the next one !!!
//
//  * Modify the gcd method so it passes all tests QUICKLY. 
//
//    Hint: Use this IDEA
//        instead of "A = A - B;", 
//        use:       "A = A % B;", 
//    which has the effect of subtracting as many copies of B 
//    as possible, at once.
//
//  * Add a comment before the method "gcd" (the first method), 
//    so that a reasonable description shows up in the editor 
//    "Documentation" view.  
//    How to do it:
//        In the BlueJ editor, click "Edit" 
//        and then "Add method comment" to get started on this.

public class Euclid3
{

    // Method gcd(A,B) implements Euclid's algorithm.
    // It RETURNS the greatest common divisor of A and B.
    public static int gcd(int A, int B)
    {
        while ( A != 0 && B != 0 )
        {
            if ( A >= B )
                A = A - B;
            else
                B = B - A;

            /* ----------------------------------------------------------
               If you want to see what's is going on in the "gcd" method,
	       you can uncomment the println statement on the next line 
	       to print A and B inside loop:
               ---------------------------------------------------------- */
            //System.out.println("A=" + A + "  B=" + B);
        }

        return B;     // Return the GCD.
    }

    // ------------------------------------------------------
    // Do NOT change these 2 methods below !!!!
    // ------------------------------------------------------

    /**
     * Method testGcd(A,B,G) tests whether gcd(A,B) returns 
     * the expected value G.
     * It prints out a message indicating whether the gcd method passed 
     * this test.
     *
     * @param A a non-negative integer
     * @param B a non-negative integer
     * @param G the expected value of gcd(A,B)
     * @return Indicates whether gcd(A,B) returned the expected value G.
     */
    public static boolean testGcd(int A, int B, int G)
    {
        System.out.print("Calling gcd(" + A + ", " + B + ") ... ");

        int result = gcd(A, B);

        if (result == G) 
        {
            System.out.println("GCD = " + result + ", good.");
            return true;	// true means "test successful"
        } 
	else 
        {
            System.out.println("GCD = " + result + " not " + G + ", ERROR!");
            return false;	// false means "test failed"
        }
    }

   /**
    * Method main is our main entry point.
    *
    * It runs several gcd test cases, using testGcd, and finally
    * prints out a summary of how many tests were pass or fail.
    *
    * @param args ignored
    */
   public static void main(String args[])
   {
       // Run several gcd test cases, like codingbat.com

       int pass = 0;            // number of passed tests
       int fail = 0;            // number of failed tests

       /* -----------------------------------------------------------
	  Now we run many tests...
	  Example:

              if  testGcd(36, 28, 4) returns true, 
		  we increment pass by 1
	      otherwise 
		  we increment fail by 1.

	  And so on
	  ---------------------------------------------------------- */
       if (testGcd(36, 28, 4))      { ++pass; } else { ++fail; }
       if (testGcd(28, 36, 4))      { ++pass; } else { ++fail; }
       if (testGcd(255, 190, 5))    { ++pass; } else { ++fail; }
       if (testGcd(0, 5, 5))        { ++pass; } else { ++fail; }
       if (testGcd(7, 0, 7))        { ++pass; } else { ++fail; }

       // ==============================================================
       // These two are slow now!
       // ==============================================================
       if (testGcd(2100000001,2,1)) { ++pass; } else { ++fail; }
       if (testGcd(3,2100000000,3)) { ++pass; } else { ++fail; }

       System.out.println("Passed " + pass + " tests out of " + (pass+fail) );
       System.out.println();
   }
}