Question

I have a recursive Tower of Hanoi program and would like to get the index numbers to be in correct sequence: 1,2,3,4,5,6,7. How can I do this?

Main.java

import java.io.*;

import java.util.List;

import java.util.Scanner;

public class Main {

public static void main(String[] args){

/**There is a stack of N disks on the first of three poles (call them A, B and C) and your job is to move the disks from pole A to pole C without ever putting a larger disk on top of a smaller disk.*/

System.out.println("\nW7L1 Tower of Hanoi");

System.out.println("Program by Quang Pham\n");

char startingrod = ' ';

char endingrod = ' ';

Scanner sc = new Scanner(System.in);

System.out.println("Enter the starting rod letter (A, B, or C).");

startingrod = sc.next().charAt(0);

System.out.println("Enter the ending rod letter (A, B, C).");

endingrod = sc.next().charAt(0);

if (startingrod == endingrod)

{

System.out.println("Sorry. Starting rod and ending rod cannot be the same.");

System.out.println("Enter ending rod letter (A, B, C)");

endingrod = sc.next().charAt(0);

}

else if ((startingrod=='A' && endingrod=='C')||(startingrod=='C' && endingrod=='A'));

{

char other = (char)('A' + 'B' + 'C' - startingrod - endingrod) ;

System.out.println("OK. Starting with disks 1, 2, 3, on rod " + startingrod + "." + "\n");

System.out.println("Moves are as follows:");

int count = playHanoi (3,startingrod,other,endingrod);

System.out.println();

System.out.printf("All disks 1, 2, 3 are on rod %c.\n", endingrod);

System.out.println("All done.");

System.out.println("Took a total of " + count + " moves.");

sc.close();

System.out.println();

}

}

private static int playHanoi( int n, char from , char other, char to)

{

int index = 1;

int count = 1;

if (n == 0)

return 0;

else if(n == 1)

{

System.out.printf("%d.", index);

System.out.printf(" Move disk "+ n +" from rod %c to rod %c \n", from, to);

index++;

return count;

}

else

{

count+= playHanoi(n - 1, from, to, other);

System.out.printf("%d.", index);

System.out.printf(" Move disk " + n + " from rod %c to rod %c \n", from, to);

index++;

count+= playHanoi(n - 1, other, from, to);

index++;

return count;

}

}

}

The program is at:  https://repl.it/@quangnvpham1/W7L1-Recursive-Tower-of-Hanoi-Program#Main.java .

Any help with this problem is greatly appreciated. Yours truly, Quang Pham

Answer 1

I run your code and get your point . Please attach output always if you do have problem in that .

As you mentioned you want to get the index numbers in correct sequence :-

One alternative for that is make your index global and static so that value of it remains unchanged or i can say constant while moving back in recursion. For code you can see below:-

import java.io.*;

import java.util.List;

import java.util.Scanner;

public class Main {

static int index=1; // Firstly i make the index variable global and initializing it with 1 as value.

public static void main(String[] args){

/**There is a stack of N disks on the first of three poles (call them A, B and C) and your job is to move the disks from pole A to pole C without ever putting a larger disk on top of a smaller disk.*/

System.out.println("\nW7L1 Tower of Hanoi");

System.out.println("Program by Quang Pham\n");

char startingrod = ' ';

char endingrod = ' ';

Scanner sc = new Scanner(System.in);

System.out.println("Enter the starting rod letter (A, B, or C).");

startingrod = sc.next().charAt(0);

System.out.println("Enter the ending rod letter (A, B, C).");

endingrod = sc.next().charAt(0);

if (startingrod == endingrod)

{

System.out.println("Sorry. Starting rod and ending rod cannot be the same.");

System.out.println("Enter ending rod letter (A, B, C)");

endingrod = sc.next().charAt(0);

}

else if ((startingrod=='A' && endingrod=='C')||(startingrod=='C' && endingrod=='A'));

{

char other = (char)('A' + 'B' + 'C' - startingrod - endingrod) ;

System.out.println("OK. Starting with disks 1, 2, 3, on rod " + startingrod + "." + "\n");

System.out.println("Moves are as follows:");

int count = playHanoi (3,startingrod,other,endingrod);

System.out.println();

System.out.printf("All disks 1, 2, 3 are on rod %c.\n", endingrod);

System.out.println("All done.");

System.out.println("Took a total of " + count + " moves.");

sc.close();

System.out.println();

}

}

private static int playHanoi( int n, char from , char other, char to)

{

// int index = 1;

int count = 1;

if (n == 0)

return 0;

else if(n == 1)

{

System.out.printf("%d.", index);

System.out.printf(" Move disk "+ n +" from rod %c to rod %c \n", from, to);

index++;

return count;

}

else

{

count+= playHanoi(n - 1, from, to, other);

System.out.printf("%d.", index);

System.out.printf(" Move disk " + n + " from rod %c to rod %c \n", from, to);

index++;

count+= playHanoi(n - 1, other, from, to);

index--; // I just decrease the count of index by 1 as it will increase two times in the recursion due to //which it skips index 4 always.

index++;

return count;

}

}

}

While running the code just remove the comments and the code will work fine.