COP 3337
Section U05
Spring 2016



                                  THE TOWERS OF HANOI
                                  ===================



   The program:




public class Hanoi {

    // test the towers of Hanoi
    public static void main(String[] args) 
    {
        System.out.println("The Towers of Hanoi");
        System.out.println("===================\n\n\n");
        
        
        // test the problem for n=3
        System.out.println("We test the problem for n = 3.");
        System.out.println("We move the 3 disks from A to C, using B.\n");
        hanoi(3,'A','C','B');
        
        // test the problem for n=4
        System.out.println("\nWe test the problem for n = 4.");
        System.out.println("We move the 4 disks from A to C, using B.\n");
        hanoi(4,'A','C','B');
        
    }
    
    // this program solves the towers of hanoi problem
    private static void hanoi(int n, char from, char to, char aux)
    {
        if (n <= 0 )
        {    
            // print error message
            System.out.println("The number must be positive!");
            return;
        }
        
        if (n == 1)
        {
            System.out.println("Move disk 1 from " + from + " to " + to + ".");
        }    
        
        else // recurse
        {
            // move n-1 disks from to to aux
            hanoi(n-1,from,aux,to);
            // move the big disk to to
            System.out.println("Move disk " + n + " from " + from + " to " + to + ".");
            // move the n-1 disks from aux to to
            hanoi(n-1, aux, to, from);
        }    
    }
}


The output:

run:
The Towers of Hanoi
===================



We test the problem for n = 3.
We move the 3 disks from A to C, using B.

Move disk 1 from A to C.
Move disk 2 from A to B.
Move disk 1 from C to B.
Move disk 3 from A to C.
Move disk 1 from B to A.
Move disk 2 from B to C.
Move disk 1 from A to C.

We test the problem for n = 4.
We move the 4 disks from A to C, using B.

Move disk 1 from A to B.
Move disk 2 from A to C.
Move disk 1 from B to C.
Move disk 3 from A to B.
Move disk 1 from C to A.
Move disk 2 from C to B.
Move disk 1 from A to B.
Move disk 4 from A to C.
Move disk 1 from B to C.
Move disk 2 from B to A.
Move disk 1 from C to A.
Move disk 3 from B to C.
Move disk 1 from A to B.
Move disk 2 from A to C.
Move disk 1 from B to C.
BUILD SUCCESSFUL (total time: 6 seconds)