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Stack using Queues
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Stack using Queues
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/* Program to implement a stack using two queue*/
#include <bits/stdc++.h>
using namespace std;
class Stack
{
queue<int> q1, q2; // Two inbuilt queues
int curr_size; // To maintain current number of elements
public:
Stack()
{
curr_size = 0;
}
void push(int x)
{
curr_size++;
// Push x first in empty q2
q2.push(x);
// Push all the remaining elements in q1 to q2.
while (!q1.empty()) {
q2.push(q1.front());
q1.pop();
}
// swap the names of two queues
queue<int> q = q1;
q1 = q2;
q2 = q;
}
void pop()
{
// if no elements are there in q1
if (q1.empty())
return;
q1.pop();
curr_size--;
}
int top()
{
if (q1.empty())
return -1;
return q1.front();
}
int size()
{
return curr_size;
}
};
int main()
{
Stack s;
s.push(1);
s.push(2);
s.push(3);
cout << "current size: " << s.size()
<< endl;
cout << s.top() << endl;
s.pop();
cout << s.top() << endl;
s.pop();
cout << s.top() << endl;
cout << "current size: " << s.size()
<< endl;
return 0;
}