QueueStack.cs

using System;
using System.Collections.Generic;

namespace AlgorithmsAndDataStructures.DataStructures.Stack;

public class QueueStack<T>
{
    private readonly Queue<T> leftQueue;
    private readonly Queue<T> rightQueue;

    public QueueStack()
    {
        leftQueue = new Queue<T>();
        rightQueue = new Queue<T>();
    }

    public bool IsEmpty => rightQueue.Count == 0 && leftQueue.Count == 0;

    public void Push(T value)
    {
        if (leftQueue.Count > 0)
            leftQueue.Enqueue(value);
        else if (rightQueue.Count > 0)
            rightQueue.Enqueue(value);
        else
            leftQueue.Enqueue(value);
    }

    public T Pop()
    {
        if (IsEmpty) throw new ArgumentException("Stack is Empty");

        return GetPopQueue().Dequeue();
    }

    public T Peak()
    {
        if (IsEmpty) throw new ArgumentException("Stack is Empty");

        return GetPopQueue().Peek();
    }

    private Queue<T> GetPopQueue()
    {
        if (leftQueue.Count > 0)
        {
            while (leftQueue.Count > 1) rightQueue.Enqueue(leftQueue.Dequeue());

            return leftQueue;
        }

        if (rightQueue.Count > 0)
        {
            while (rightQueue.Count > 1) leftQueue.Enqueue(rightQueue.Dequeue());

            return rightQueue;
        }

        throw new ArgumentException("Stack is Empty");
    }
}