stack using queue cpp

 Implementing stack using queue

Two methods to solve this 

1-) Making push method costly

2-) Making Pop method costly

1- Making Push operation costly

Logic-

First make two queues then you want to push elements into the queue so first pushed element will store in the q2 and then add all the element from q1 to  with q2 and then swap it to q1 and the process continues till last element .

for better explanation please watch out the video  

  Must watch out this video to understand the logic with visualization and animation so must watch it.

Coding

#include <bits/stdc++.h>

using namespace std;

class Stack

{

public:
    int N;

    queue<int> q1;

    queue<int> q2;

    Stack() // constructor

    {

        N = 0; // size initialize with 0
    }

    void push(int val)

    {

        q2.push(
            val); // according to our algo we first enter
                  // our push value into second queue

        while (!q1.empty())

        {

            q2.push(q1.front());

            // then according to algo now we have to put all
            // the element that is present in q1 add into q2
            // till q1 is not empty

            q1.pop(); // pop that element from q1
        }

        // to swap

        queue<int> temp = q1; // make a temporary queue

        q1 = q2;

        q2 = temp;
    }

    void pop()

    {

        q1.pop();

        N--;
    }

    // find top value

    int top() { return q1.front(); }

    // give the current size of stack

    int size() { return N; }
};

int main()

{

    Stack st;

    st.push(2);

    st.push(5);

    st.push(8);

    st.push(4);

    cout << st.top() << endl;

    st.pop();

    cout << st.top() << endl;

    st.pop();

    cout << st.top() << endl;

    st.pop();

    cout << st.top() << endl;

    st.pop();

    st.pop();

    cout << st.size() << endl;

    return 0;
}

2-) Making Pop method costly

Logic-

First make two queues then you have to then push values into q1 then here is the important step for this step 2 so we have to pop the top element (first the value insert into queue)  from the stack and add the rest values into Q2 and then swap it

for better explanation please watch out the video  

  Must watch out this video to understand the logic with visualization and animation so must watch it.

Coding

#include <bits/stdc++.h>
using namespace std;
class Stack
{
    int N;
    queue<int> q1;
    queue<int> q2;
public:
    Stack() //constructor
    {
        N = 0; //size initialize with 0
    }
    void pop()
    {
        if (q1.empty()) //check there if something is present
        {
            return;
        }
        while (q1.size() != 1) //jabtak q1 ek value nhi bach ta tab tak continue
        {
            q2.push(q1.front()); //and add into q2
            q1.pop();            //then pop it
        }
        q1.pop();
        N--;
        //to swap
        queue<int> temp = q1; //make a temporary queue
        q1 = q2;
        q2 = temp;
    }
    void push(int val)
    {
        q1.push(val);
        N++;
    }
    // Top value
    int top()
    {
        if (q1.empty())
        {
            return -1;
        }
        while (q1.size() != 1)
        {
            q2.push(q1.front());
            q1.pop();
        }
        int ans = q1.front();
        q2.push(ans);
        //to swap
        queue<int> temp = q1; //make a temporary queue
        q1 = q2;
        q2 = temp;
        return ans;
    }
    int size()
    {
        return N;
    }
};
int main()
{
    Stack st;
    st.push(1);
    st.push(3);
    st.push(7);
    st.push(9);
    cout << st.top() << endl;
    st.pop();
    cout << st.top() << endl;
    cout << st.size() << endl;
}