Question

How to reverse a stack using a queue?
Preferably share the sample C code?

Answer 1

Its same as reversing the stack using the stack. Simply pop and put into the rear of the queue till last element. Now pick from the front of the queue and push into the stack and you are done.

See the following sample implementation which I found on the Internet -

#include<conio.h>
#include<stdio.h>

#define MAX 100

void show(int stack[],int size,int top)
{
    int i;
    for(i=0;i<size;i++)
    {
        printf("\nValue at %d is %d",top,stack[top]);
        top=top-1;
    }
}

void reverse(int stack[],int qu[],int *t,int *r,int *f)
{
    *f=0;
    while(*t>-1)
    {
        *r=*r+1;
        qu[*r]=stack[*t];
        *t=*t-1;
    }
    while(*f<=*r)
    {
        *t=*t+1;
        stack[*t]=qu[*f];
        *f=*f+1;
    }
}

void main()
{
    int size;
    int item,t,i,stack[MAX],quee[MAX];
    int top=-1,front=-1,rear=-1;

    printf("Enter size of stack::");
    scanf("%d",&size);

    for(i=0;i<size;i++)
    {
        top=top+1;
        printf("Enter value of for position %d ::",top);
        scanf("%d",&item);
        stack[top]=item;
    }

    show(stack,size,top);
    reverse(stack,quee,&top,&rear,&front);

    printf("\nAfter reverse..............");
    show(stack,size,top);

    getch();
}