Add shuffle logic to Deck class

CSharp/Blackbaud.Interview.Cards/Deck.cs

@@ -57,5 +57,16 @@ public Card NextCard()
             return null;
         }
     }
+    public void ShuffleCards(IShuffler shuffler, int? shuffleRounds = null, int? seed = null)
+    {
+        if(shuffler is null) throw new ArgumentNullException(nameof(shuffler));
+        var cards=_stackOfCards.Reverse().ToList();
+        shuffler.shuffle(cards,shuffleRounds,seed);
+        _stackOfCards.Clear();
+        foreach(var card in cards)
+        {
+            _stackOfCards.Push(card);
+        }
+    }
 
 }

CSharp/Blackbaud.Interview.Cards/Program.cs

@@ -11,10 +11,10 @@ static void Main()
 
         // Create a new deck
         var deck = Deck.NewDeck();
-
+        IShuffler shuffler=new FisherYatesShuffler();
         // TODO: shuffle the deck
         Console.WriteLine("Shuffling...");
-
+        deck.ShuffleCards(shuffler,shuffleRounds:100,seed:null);
         // Deal all the cards
         while (!deck.Empty)
         {

CSharp/Blackbaud.Interview.Cards/Shuffler/IShuffler.cs

@@ -0,0 +1,6 @@
+namespace Blackbaud.Interview.Cards.Shuffler;
+
+public interface IShuffler
+{
+    void shuffle(IList<Card> cards,int?shuffleRounds=null,int?seed=null);
+}

CSharp/Blackbaud.Interview.Cards/Shuffler/Shuffler.cs

@@ -0,0 +1,32 @@
+namespace Blackbaud.Interview.Cards.Shuffler;
+
+public class FisherYatesShuffler : IShuffler
+{
+    public void shuffle(IList<Card> cards, int? shuffleRounds = null, int? seed = null)
+    {
+        if(cards is null) throw new ArgumentNullException(nameof(cards));
+        int n=cards.Count;
+        Random rand = seed.HasValue ? new Random(seed.Value) : new Random();
+        if(shuffleRounds==null)
+        {
+            for(int i=n-1;i>0;i--)
+            {
+                int j=rand.Next(i+1);
+                (cards[i],cards[j])=(cards[j],cards[i]);
+            }
+        }
+        else
+        {
+            int rounds=shuffleRounds.Value;
+            for(int r = 0; r < rounds; r++)
+            {
+                int i=rand.Next(n);
+                int j=rand.Next(n);
+                if(i==j) continue;
+                (cards[i],cards[j])=(cards[j],cards[i]);
+            }
+        }
+    }
+
+
+}