chore(CSharp): add implementation of queue using two stacks (#448)

Co-authored-by: Ming Tsai <37890026+ming-tsai@users.noreply.github.com>

algorithms/CSharp/README.md

@@ -17,8 +17,11 @@ For running the `.cs` file please using [.Net Finddle](https://dotnetfiddle.net/
 ## Maths
 - [Abundant Number](src/Maths/abundant-number.cs)
 
+## Queues
+- [Queue Implementation Using Two Stacks](src/Queues/queue-implementation-using-two-stacks.cs)
+
 ## Recusrsion
 - [Factorial](src/Recursion/factorial.cs)
 
 ## Graph
-- [Depth First Search](src/Graph/depth-first-search.cs)
+- [Depth First Search](src/Graph/depth-first-search.cs)

algorithms/CSharp/src/Queues/queue-implementation-using-two-stacks.cs

@@ -0,0 +1,87 @@
+using System;
+using System.Collections.Generic;
+
+namespace Algorithms.Queues
+{
+    public class QueueImplementationUsingTwoStacks
+    {
+        public class MyQueue<T>
+        {
+            private Stack<T> _stack1, _stack2;
+            
+            public MyQueue()
+            {
+                _stack1 = new Stack<T>();
+                _stack2 = new Stack<T>();
+            }
+
+            public void Push(T x)
+            {
+                _stack1.Push(x);
+            }
+
+            public T Pop()
+            {
+                if (Empty())
+                {
+                    throw new InvalidOperationException();
+                }
+
+                if(_stack2.Count > 0)
+                {
+                    return _stack2.Pop();
+                }
+
+                while(_stack1.Count > 0)
+                {
+                    _stack2.Push(_stack1.Pop());
+                }
+
+                return _stack2.Pop();
+            }
+
+            public T Peek()
+            {
+                if (Empty())
+                {
+                    throw new InvalidOperationException();
+                }
+
+                if (_stack2.Count > 0)
+                {
+                    return _stack2.Peek();
+                }
+
+                while (_stack1.Count > 0)
+                {
+                    _stack2.Push(_stack1.Pop());
+                }
+
+                return _stack2.Peek();
+            }
+
+            public bool Empty()
+            {
+                return _stack1.Count == 0 && _stack2.Count == 0;
+            }
+
+            public int Count()
+            {
+                return _stack1.Count + _stack2.Count;
+            }
+        }
+
+        public static void Main()
+        {
+            MyQueue<int> myQueue = new MyQueue<int>();
+            
+            myQueue.Push(3);
+            myQueue.Push(4);
+            Console.Write($"{myQueue.Peek()} ");
+            myQueue.Pop();
+            Console.Write($"{myQueue.Peek()} ");
+            myQueue.Push(7);
+            Console.Write($"{myQueue.Peek()} ");
+        }
+    }
+}

algorithms/CSharp/test/Queues/queue-implementation-using-two-stacks.cs

@@ -0,0 +1,43 @@
+using NUnit.Framework;
+using System.Collections.Generic;
+
+namespace Algorithms.Tests.Queues
+{
+    [TestFixture]
+    class QueueImplementationUsingTwoStacks
+    {
+        [Test]
+        public void TestQueueUsingTwoStacks1_ShouldGetExpectedResult()
+        {
+            Algorithms.Queues.QueueImplementationUsingTwoStacks.MyQueue<int> myQueue;
+            myQueue = new Algorithms.Queues.QueueImplementationUsingTwoStacks.MyQueue<int>();
+
+            List<int> result = new List<int>();
+
+            myQueue.Push(7);
+            result.Add(myQueue.Peek());
+            result.Add(myQueue.Count());
+
+            myQueue.Push(118);
+            result.Add(myQueue.Count());
+            result.Add(myQueue.Peek());
+
+            myQueue.Push(107);
+            result.Add(myQueue.Count());
+            result.Add(myQueue.Peek());
+
+            myQueue.Pop();
+            result.Add(myQueue.Peek());
+            result.Add(myQueue.Count());
+
+            myQueue.Pop();
+            result.Add(myQueue.Peek());
+            result.Add(myQueue.Count());
+
+            myQueue.Pop();
+            result.Add(myQueue.Count());
+
+            Assert.AreEqual("7 1 2 7 3 7 118 2 107 1 0", string.Join(" ", result));
+        }
+    }
+}