Implement Stack using Queues.cpp

/* 

    Solution by Rahul Surana

    ***********************************************************

Implement a last in first out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal queue (push, top, pop, and empty).

Implement the MyStack class:

void push(int x) Pushes element x to the top of the stack.
int pop() Removes the element on the top of the stack and returns it.
int top() Returns the element on the top of the stack.
boolean empty() Returns true if the stack is empty, false otherwise.
Notes:

You must use only standard operations of a queue, which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue), as long as you use only a queue's standard operations.


    ***********************************************************
*/


#include <bits/stdc++.h>
#define ll          long long
#define vl          vector<ll>
#define vi          vector<int>
#define pi          pair<int,int>
#define pl          pair<ll,ll>
#define all(a)      a.begin(),a.end()
#define mem(a,x)    memset(a,x,sizeof(a))
#define pb          push_back
#define mp          make_pair
#define F           first
#define S           second
#define FOR(i,a)     for(int i = 0; i < a; i++)
#define trace(x)    cerr<<#x<<" : "<<x<<endl;
#define trace2(x,y) cerr<<#x<<" : "<<x<<" | "<<#y<<" : "<<y<<endl;
#define trace3(x,y,z) cerr<<#x<<" : "<<x<<" | "<<#y<<" : "<<y<<" | "<<#z<<" : "<<z<<endl;
#define fast_io     std::ios::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL)
#define MOD 1000000007 
using namespace std;

class MyStack {
public:
    
    queue<int> q1,q2;
    
    /** Initialize your data structure here. */
    MyStack():q1(),q2() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        q1.push(x);
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        
        int out;
        while(!q1.empty()){
            q2.push(q1.front());
            // cout << q1.front()<<"\n";
            out = q1.front();
            q1.pop();
             
        }
        int n = q2.size();
        while(!q2.empty()){
            if(n > q1.size()+1)
            q1.push(q2.front());
            q2.pop();
        }
        return out;
    }
    
    /** Get the top element. */
    int top() {
        int out;
        while(!q1.empty()){
            q2.push(q1.front());
            // cout << q1.front()<<"\n";
            out = q1.front();
            q1.pop();
        }
        while(!q2.empty()){
            q1.push(q2.front());
            q2.pop();
        }
        return out;
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        cout << q1.size()<<"\n";
        return q1.empty();
    }
};

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack* obj = new MyStack();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->top();
 * bool param_4 = obj->empty();
 */

int main()
{
    fast_io;
    MyStack x;

}