Tower of Hanoi C++(using recursion)

Ishaan Sharma picture Ishaan Sharma · Aug 26, 2013 · Viewed 18.6k times · Source

I wrote the following code as a practice exercise.
I'm getting incorrect output when I print the destination stack.
Can anyone please point out where I'm going wrong ?

//Tower of Hanoi using Stacks!
#include<iostream.h>
#include<conio.h>
#include<stdlib.h>

class Stack
{
private:
    int *t;
    int length, top;

public:
    Stack(int len)
    {
        length=len;
        t= new int[len];
        top=-1;
    }

    ~Stack()
    {
        delete []t;
    }

    void push(int d)
    {
        top++;
        t[top]=d;
    }

    int pop()
    {
        top--;
        return t[top+1];
    }

    void printstack()
    {
        int cur=top;
        while(cur>-1)
        {
            cout<<t[cur]<<endl;
            cur--;
        }
    }
};

void MoveTowerofHanoi(int disk, Stack *source, Stack *temp, Stack *destination)
{
    if (disk==0)
    {
        destination->push(source->pop());
    }
    else
    {
        MoveTowerofHanoi(disk-1,source,temp,destination);
        destination->push(source->pop());
        MoveTowerofHanoi(disk-1,temp,destination,source);
    }
}

void main()
{
    clrscr();
    int disks;
    cout<<"Enter the number of disks!"<<endl;
    cin>>disks;
    Stack* source=new Stack(disks);
    for(int i=0; i<disks; i++) {
        source->push(disks-i);
    }
    cout<<"Printing Source!"<<endl;
    source->printstack();
    Stack* temp=new Stack(disks);
    Stack* destination=new Stack(disks);
    MoveTowerofHanoi(disks,source,temp,destination);
    cout<<"Printing Destination!"<<endl;
    destination->printstack();
    getch();
}

Here's the output I'm getting:

Enter the no. of disks!  
3  
Printing Source!  
1  
2  
3  
Printing Destination!  
-4

After editing, the code looks like this:

    void MoveTowerofHanoi(int disk, Stack *source, Stack *destination, Stack *temp)
{
    if (disk==1)
    {
        destination->push(source->pop());
    }
    else
    {
        MoveTowerofHanoi(disk-1,source,temp,destination);
        destination->push(source->pop());
        MoveTowerofHanoi(disk-1,temp,destination,source);
    }
}

the first mistake was:

void MoveTowerofHanoi(int disk, Stack *source, Stack *temp, Stack *destination)

the second was:

if (disk==0)

Many thanks to all for helping!


Changes made to stack class:

void push(int d)
{
     if(top<length-1)
    {
    top++;
    t[top]=d;
    }

}

int pop()
{
    if(top>-1)
    {
    top--;
    return t[top+1];
    }
}

Answer

cpp picture cpp · Aug 26, 2013

This works:

//Tower of Hanoi using Stacks!
#include<iostream>
//#include<conio.h>
#include<stdlib.h>
#include<vector>
#include<algorithm>
using namespace std;

void print_elem(int elem)
{
    cout << elem << endl;       
}

class Stack{
public:
    void push(int d){t.push_back(d);}
    int pop()
    {
        int d=t.back();
        t.pop_back();
        return d;
    }
    void printstack()
    {
        for_each(t.rbegin(),t.rend(),print_elem);
    }
private:
    vector<int> t;

};

void MoveTowerofHanoi(int disk, Stack *source, Stack *temp, Stack *destination)
{
    if (disk==1)
    {
        destination->push(source->pop());
    }
    else
    {
        MoveTowerofHanoi(disk-1,source,destination,temp);
        destination->push(source->pop());
        MoveTowerofHanoi(disk-1,temp,source,destination);
    }
}

int main()
{
    int disks;
    cout<<"Enter the number of disks!"<<endl;
    cin>>disks;
    Stack* source = new Stack();
    for(int i=disks; i>0; --i) {
        source->push(i);
    }

    cout<<"Printing Source!"<<endl;
    source->printstack();
    Stack* temp = new Stack();
    Stack* destination = new Stack();
    MoveTowerofHanoi(disks,source,temp,destination);
    cout<<"Printing Destination!"<<endl;
    destination->printstack();
    delete source;
    delete temp;
    delete destination;
}