Question

Tower of Hanoi - Java Code

• Use three rods labeled A, B, and C
• Use three discs labels 1 (smallest), 2 (medium size), and 3 (largest disc)
• The program prompts you to enter the starting rod (A, B, or C)
• The program prompts you to enter the ending rod (A, B, or C, but cannot be same rod as entered as starting rod)
• The starting rod has discs 1, 2, 3, where 1 is on top of 2 is on top of 3 (just like we covered in class)
• Your program should print out each move, showing clearly which disc goes from/to. See trace below.

Example output

Tower of Hanoi
Program by YOUR NAME
Enter Starting Rod  (A, B, or C): A
Enter Ending Rod (A, B, or C): A
Sorry.  starting and ending rod cannot be the same.
Enter Ending Rod ((A, B, or C): C
OK Starting with  discs 1, 2, and 3 on rod A
Moves are as follows:
1. Move disc 1 from rod A to rod C
2. Move disc 2 from rod A to rod B
3. Move disc 1 from rod C to rod B
4. Move disc. 3 from rod A to rod C
5. Move disk 1 from rod B to rod A
6. Move disk 2 from rod B to rod C
7. Move disk 1 from rod A to rod C
All done. Took a total of 7 moves.

Answer 1

Hello,

• The program has been implemented below in Java.
• The error handling cases have been taken care of.
• Appropriate comments have been added for better understanding of the user.
• Below is the code, code snippet ( for indentation purposes) and output.

Code:

import java.util.Scanner;
public class TOH 
{ 
    // Recursive function to solve Tower of Hanoi
    static int towerOfHanoi(int n, String start_rod, String end_rod, String aux_rod, int moves)
    {   
        if(n>0){
            if (n == 1) 
            { 
                System.out.println("Move disk 1 from rod " +  start_rod + " to rod " + end_rod); 
                return moves; 
            } 
            
            moves = towerOfHanoi(n-1, start_rod, aux_rod, end_rod, moves); 
            System.out.println("Move disk " + n + " from rod " +  start_rod + " to rod " + end_rod);
            moves ++;
            
            moves = towerOfHanoi(n-1, aux_rod, end_rod, start_rod, moves); 
            moves ++;
        }
        return moves;
    } 
      
    //  Main method 
    public static void main(String args[]) 
    { 
        // Take start and end rod as input from the user
        
        Scanner scanner = new Scanner (System.in);
        System.out.print("Enter Starting Rod  (A, B, or C): ");  
        String start_rod = scanner.next().toUpperCase();
        System.out.println(start_rod); 
        
        System.out.print("Enter Ending Rod  (A, B, or C): ");  
        String end_rod = scanner.next().toUpperCase();
        System.out.println(end_rod); 
        
        // Check if the user enters same start and end rod
        
        while (start_rod.equals(end_rod))
        {
            System.out.println("Sorry.  starting and ending rod cannot be the same. "); 
            System.out.print("Enter Ending Rod  (A, B, or C): ");  
            end_rod = scanner.next().toUpperCase();
            System.out.println(end_rod); 
        }
        
        // Finding the aux rod
        String aux_rod;
        
        if ((start_rod.equals("A") && end_rod.equals("C")) || (start_rod.equals("C") && end_rod.equals("A")))
        {
            aux_rod = "B";
        }
        else if ((start_rod.equals("B") && end_rod.equals("C")) || (start_rod.equals("C") && end_rod.equals("B")))
        {
            aux_rod = "A";
        }
        else
        {
            aux_rod = "C";
        }
        
        int n = 3; // Number of disks as defined in the question
        int moves = 1; // Minimum number of moves to count the number of steps taken.
        int count = towerOfHanoi(n, start_rod, end_rod, aux_rod, moves); 
        System.out.println("All done. Took a total of " + count +  " moves");
    } 
} 

Code Snippet:

Output:

$javac TOH.java
$java -Xmx128M -Xms16M TOH
Enter Starting Rod  (A, B, or C): A
Enter Ending Rod  (A, B, or C): A
Sorry.  starting and ending rod cannot be the same. 
Enter Ending Rod  (A, B, or C): B
Move disk 1 from rod A to rod B
Move disk 2 from rod A to rod C
Move disk 1 from rod B to rod C
Move disk 3 from rod A to rod B
Move disk 1 from rod C to rod A
Move disk 2 from rod C to rod B
Move disk 1 from rod A to rod B
All done. Took a total of 7 moves