Implement Stack using Queues

/* C# Program to implement a stack using
two queue */
using System;
using System.Collections;

class GfG {

    public class Stack {
        // Two inbuilt queues
        public Queue q1 = new Queue();
        public Queue q2 = new Queue();

        public void push(int x)
        {
            // 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();
        }

        public int top()
        {
            if (q1.Count == 0)
                return -1;
            return (int)q1.Peek();
        }

        public int size() { return q1.Count; }
    };

    // 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());
    }
}

// This code is contributed by Arnab Kundu

using System;
using System.Collections;
class GfG {
    public class Stack {
        public Queue q1 = new Queue();
        public Queue q2 = new Queue();
        // Just enqueue the new element to q1
        public void Push(int x) = > q1.Enqueue(x);

        // move all elements from q1 to q2 except the rear
        // of q1. Store the rear of q1 swap q1 and q2 return
        // the stored result
        public int Pop()
        {
            if (q1.Count == 0)
                return -1;
            while (q1.Count > 1) {
                q2.Enqueue(q1.Dequeue());
            }
            int res = (int)q1.Dequeue();
            Queue temp = q1;
            q1 = q2;
            q2 = temp;
            return res;
        }

        public int Size() = > q1.Count;

        public int Top()
        {
            if (q1.Count == 0)
                return -1;
            while (q1.Count > 1) {
                q2.Enqueue(q1.Dequeue());
            }
            int res = (int)q1.Dequeue();
            q2.Enqueue(res);
            Queue temp = q1;
            q1 = q2;
            q2 = temp;
            return res;
        }
    };
    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());
    }
}

// Submitted by Sakti Prasad

/* C# Program to implement a stack using only one queue */
using System;
using System.Collections;

class GfG {

  public class Stack
  {

    // One inbuilt queue
    public Queue q = new Queue();

    public void push(int x)
    {
      // Get previous size of queue
      int s = q.Count;

      // Push the current element
      q.Enqueue(x);

      // Pop all the previous elements and put them
      // afte current element
      for (int i = 0; i < s; i++) {
        // Add the front element again
        q.Enqueue(q.Peek());

        // Delete front element
        q.Dequeue();
      }
    }

    // Removes the top element
    public void pop()
    {
      // if no elements are there in q
      if (q.Count == 0)
        Console.WriteLine("No elements");
      else
        q.Dequeue();
    }

    // Returns top of stack
    public int top()
    {
      if (q.Count == 0)
        return -1;
      return (int)q.Peek();
    }

    public int size() { return q.Count; }
  };

  // Driver code
  public static void Main(String[] args)
  {
    Stack st = new Stack();
    st.push(1);
    st.push(2);
    st.push(3);
    Console.WriteLine("current size: " + st.size());
    Console.WriteLine(st.top());
    st.pop();
    Console.WriteLine(st.top());
    st.pop();
    Console.WriteLine(st.top());
    Console.WriteLine("current size: " + st.size());
  }
}

// This code is contributed by Susobhan Akhuli

// C# Program to implement a stack
// using one queue and recursion

using System;
using System.Collections;

class GfG {

    public class Stack {
        // One inbuilt queue
        public Queue q = new Queue();

        // Push operation
        public void push(int x, int c)
        {

            // Push the current element first and
            // After every recursion add the front element
            // again
            q.Enqueue(x);

            // Return if size becomes 0
            if (c <= 0)
                return;

            // Store current front
            int p = (int)q.Peek();

            // Delete front element
            q.Dequeue();

            // Decrement size by 1 in every recursion
            c--;
            push(p, c);
        }

        // Removes the top element
        public void pop()
        {
            // if no elements are there in q
            if (q.Count == 0)
                Console.WriteLine("No elements");
            else
                q.Dequeue();
        }

        // Returns top of stack
        public int top()
        {
            if (q.Count == 0)
                return -1;
            return (int)q.Peek();
        }

        public int size() { return q.Count; }
    };

    // Driver code
    public static void Main(String[] args)
    {
        Stack st = new Stack();
        st.push(1, st.size());
        st.push(2, st.size());
        st.push(3, st.size());
        Console.WriteLine("current size: " + st.size());
        Console.WriteLine(st.top());
        st.pop();
        Console.WriteLine(st.top());
        st.pop();
        Console.WriteLine(st.top());
        Console.WriteLine("current size: " + st.size());
    }
}

// This code is contributed by Susobhan Akhuli

// C# Program to implement a stack
// using dequeue
using System;
using System.Collections.Generic;

class Stack {
    private LinkedList<int> list = new LinkedList<int>();

    public void Push(int item)
    {
        // Append the item to the end of the linked list
        list.AddLast(item);
    }

    public int Pop()
    {
        // Remove and return the item from the end of the
        // linked list
        int item = list.Last.Value;
        list.RemoveLast();
        return item;
    }

    public int Size()
    {
        // Return the size of the linked list
        return list.Count;
    }

    public bool IsEmpty()
    {
        // Return true if the linked list is empty, and
        // false otherwise
        return list.Count == 0;
    }

    public int Top()
    {
        if (IsEmpty()) {
            // If the stack is empty, return -1
            return -1;
        }
        else {
            // Return the last item in the linked list
            return list.Last.Value;
        }
    }
}

class Program {
    static void Main(string[] args)
    {
        Stack st = new Stack();
        st.Push(1);
        st.Push(2);
        st.Push(3);
        Console.WriteLine("current size: " + st.Size());
        Console.WriteLine(st.Top());
        st.Pop();
        Console.WriteLine(st.Top());
        st.Pop();
        Console.WriteLine(st.Top());
        Console.WriteLine("current size: " + st.Size());
    }
}

// This code is contributed by Susobhan Akhuli