Ashwani Blog

c code to reverse a queue by using stack

July ,7th ,2022
cstackqueue
write a c code to reverse a queue by using stack

WAP using a function to reverse a queue by using stack.

Code

#include <stdio.h>
#include <stdlib.h>

struct Node
{
    int data;
    struct Node *next;
};

struct Node *s = NULL;
struct Node *f = NULL;
struct Node *r = NULL;

void Display(struct Node *ptr)
{
    printf("Printing the elements of this linked list\n");
    while (ptr != NULL)
    {
        printf("Element: %d\n", ptr->data);
        ptr = ptr->next;
    }
}

int isEmpty(struct Node *top)
{
    if (top == NULL)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}

int isFull(struct Node *top)
{
    struct Node *p = (struct Node *)malloc(sizeof(struct Node));
    if (p == NULL)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}

struct Node *push(struct Node *top, int x)
{
    if (isFull(top))
    {
        printf("Stack Overflow\n");
    }
    else
    {
        struct Node *n = (struct Node *)malloc(sizeof(struct Node));
        n->data = x;
        n->next = top;
        top = n;
        return top;
    }
}

int pop()
{
    if (isEmpty(s))
    {
        printf("Stack Underflow\n");
    }
    else
    {
        struct Node *n = s;
        s = s->next;
        int x = n->data;
        free(n);
        return x;
    }
}

void enqueue(int val)
{
    struct Node *n = (struct Node *)malloc(sizeof(struct Node));
    if (n == NULL)
    {
        printf("Queue is Full");
    }
    else
    {
        n->data = val;
        n->next = NULL;
        if (f == NULL)
        {
            f = r = n;
        }
        else
        {
            r->next = n;
            r = n;
        }
    }
}

int dequeue()
{
    int val = -1;
    struct Node *ptr = f;
    if (f == NULL)
    {
        printf("Queue is Empty\n");
    }
    else
    {
        f = f->next;
        val = ptr->data;
        free(ptr);
    }
    return val;
}

void reverse_queue_using_stack()
{
    while (f != NULL)
    {
        s = push(s, dequeue());
    }
    while (s != NULL)
    {
        enqueue(pop());
    }
}

int main()
{

    printf("enqueuing elements\n");
    enqueue(34);
    enqueue(4);
    enqueue(7);
    enqueue(17);
    Display(f);
    reverse_queue_using_stack();
    Display(f);

    return 0;
}