Queues using stacks.cpp

#include <bits/stdc++.h>

using namespace std;
 

struct Queue {

    stack<int> s1, s2;
 

    void enQueue(int x)

    {

        // Move all elements from s1 to s2

        while (!s1.empty()) {

            s2.push(s1.top());

            s1.pop();

        }
 

        // Push item into s1

        s1.push(x);
 

        // Push everything back to s1

        while (!s2.empty()) {

            s1.push(s2.top());

            s2.pop();

        }

    }
 

    // Dequeue an item from the queue

    int deQueue()

    {

        // if first stack is empty

        if (s1.empty()) {

            cout << "Q is Empty";

            exit(0);

        }
 

        // Return top of s1

        int x = s1.top();

        s1.pop();

        return x;

    }
};
 
// Driver code

int main()
{

    Queue q;

    q.enQueue(1);

    q.enQueue(2);

    q.enQueue(3);
 

    cout << q.deQueue() << '\n';

    cout << q.deQueue() << '\n';

    cout << q.deQueue() << '\n';
 

    return 0;
}