#include "pch.h"
#include <iostream>
using namespace std;


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

struct Node* stack_push(struct Node* h, int val)
{
    struct Node* cur = (struct Node*)
        malloc(sizeof(struct Node));

    cur->val = val;
    cur->next = h;
    h = cur;

    return h;
};




struct Node* stack_pop(struct Node* h)
{
    Node* cur = h;

    if (cur != NULL)
    {
        h = cur->next;
        free(cur);
        cur->val = NULL;
        cur->next = NULL;
    }

    return h;
};


void stack_show(Node* h)
{
    Node* cur = h;
    while (cur)
    {
        cout << cur->val << " ";

        cur = cur->next;
    }

    cout << endl;
};

int main()
{
    struct Node* head = NULL;
    struct Node* tail = NULL;


    head = stack_push(head, 5);
    head = stack_push(head, 10);
    head = stack_push(head, 20);


    stack_show(head);
    head = stack_pop(head);


    stack_show(head);
    head = stack_pop(head);


    stack_show(head);
    head = stack_pop(head);

    stack_show(head);


    return 0;


}
void push_queue(struct Node* tail, int val){

    if(tail==head){
        struct Node* cur = (struct Node*)malloc(sizeof(struct Node));
        cur->val=val;
        cur->next =NULL;
        tail=cur;
        head->next = tail;
    }
    if(tail==NULL){
        head->val = tail->val = val;
        head->next = tail->next = NULL;
    }
    struct Node* cur = (struct Node*)malloc(sizeof(struct Node));
    cur->next = NULL;
    cur->val = val;
    tail->next=cur;
    tail = cur;
}

struct Node* pop_queue(struct Node* head, int val){
    Node* cur = head;
    if(head==NULL){
        cout << "queue is empty" << endl;
        return 0;
    }
    head=head->next;
    return cur;
}