ImplementStckUsingQueue.C#

using System; 
using System.Collections; 
  
class ImplementStckUsingQueue { 
  
    public class Stack { 
        // Two inbuilt queues 
        public Queue q1 = new Queue(); 
        public Queue q2 = new Queue(); 
  
        // To maintain current number of 
        // elements 
        public int curr_size; 
  
        public Stack() 
        { 
            curr_size = 0; 
        } 
  
        public void push(int x) 
        { 
            curr_size++; 
  
            // Push x first in empty q2 
            q2.Enqueue(x); 
  
            // Push all the remaining 
            // elements in q1 to q2. 
            while (q1.Count > 0) { 
                q2.Enqueue(q1.Peek()); 
                q1.Dequeue(); 
            } 
  
            // swap the names of two queues 
            Queue q = q1; 
            q1 = q2; 
            q2 = q; 
        } 
  
        public void pop() 
        { 
  
            // if no elements are there in q1 
            if (q1.Count == 0) 
                return; 
            q1.Dequeue(); 
            curr_size--; 
        } 
  
        public int top() 
        { 
            if (q1.Count == 0) 
                return -1; 
            return (int)q1.Peek(); 
        } 
  
        public int size() 
        { 
            return curr_size; 
        } 
    }; 
  
    // Driver code 
    public static void Main(String[] args) 
    { 
        Stack s = new Stack(); 
        s.push(1); 
        s.push(2); 
        s.push(3); 
        Console.WriteLine("current size: " + s.size()); 
        Console.WriteLine(s.top()); 
        s.pop(); 
        Console.WriteLine(s.top()); 
        s.pop(); 
        Console.WriteLine(s.top()); 
        Console.WriteLine("current size: " + s.size()); 
    } 
}