Fix issue #534: Modernization and refactoring: C# codebase does not leverage latest C# features

Algorithms.Tests/Other/LuhnTests.cs

@@ -56,4 +56,29 @@ public void GetLostNum(string number)
         // Assert
         Assert.That(validate, Is.True);
     }
+
+    [TestCase("")]
+    [TestCase("xxxx")] 
+    [TestCase("abcde")]
+    [TestCase("1x345678901234567")]
+    [TestCase("x1234567890123456")]
+    [TestCase("1234567890123456x")]
+    [TestCase("1111111111111111")]
+    [TestCase("1a2b3c4d5e6f7g8h9i0j")]
+    public void EdgeCases_GetLostNum(string number)
+    {
+        // Act
+        int lostNum = Luhn.GetLostNum(number.Replace("x", "0"));
+        // Assert
+        Assert.That(lostNum, Is.InRange(0, 9));
+    }
+
+    [TestCase("1a2b3c4d5e6f7g8h9i0j")]
+    public void EdgeCases_Validate(string number)
+    {
+        // Act
+        bool result = Luhn.Validate(number);
+        // Assert
+        Assert.That(result, Is.False);
+    }
 }

Algorithms/Other/Luhn.cs

@@ -31,17 +31,11 @@ public static int GetLostNum(string number)
         var missingDigitIndex = number.Length - 1 - number.LastIndexOf("x", StringComparison.CurrentCultureIgnoreCase);
         var checkDigit = GetSum(number.Replace("x", "0", StringComparison.CurrentCultureIgnoreCase)) * 9 % 10;
 
-        // Case 1: If the index of the missing digit is even.
-        if (missingDigitIndex % 2 == 0)
-        {
-            return checkDigit;
-        }
-
-        var candidateDigit = checkDigit / 2;
-
-        // Case 2: if the index of the missing digit is odd and the candidate is valid.
-        // Case 3: if the index of the missing digit is odd and we need the alternative.
-        return Validate(number.Replace("x", candidateDigit.ToString())) ? candidateDigit : (checkDigit + 9) / 2;
+        return missingDigitIndex % 2 == 0
+            ? checkDigit
+            : Validate(number.Replace("x", (checkDigit / 2).ToString()))
+                ? checkDigit / 2
+                : (checkDigit + 9) / 2;
     }
 
     /// <summary>
@@ -52,12 +46,17 @@ public static int GetLostNum(string number)
     private static int GetSum(string number)
     {
         var sum = 0;
-        for (var i = 0; i < number.Length; i++)
+        var span = number.AsSpan();
+        for (var i = 0; i < span.Length; i++)
         {
-            var digit = number[i] - '0';
-            digit = (i + number.Length) % 2 == 0
-                ? 2 * digit
-                : digit;
+            var c = span[i];
+            if (c is < '0' or > '9')
+            {
+                continue;
+            }
+
+            var digit = c - '0';
+            digit = (i + span.Length) % 2 == 0 ? 2 * digit : digit;
             if (digit > 9)
             {
                 digit -= 9;

DataStructures/BinarySearchTree/BinarySearchTree.cs

@@ -25,19 +25,9 @@ public class BinarySearchTree<TKey>
     /// </summary>
     public BinarySearchTreeNode<TKey>? Root { get; private set; }
 
-    public BinarySearchTree()
-    {
-        Root = null;
-        Count = 0;
-        comparer = Comparer<TKey>.Default;
-    }
+    public BinarySearchTree() => (Root, Count, comparer) = (null, 0, Comparer<TKey>.Default);
 
-    public BinarySearchTree(Comparer<TKey> customComparer)
-    {
-        Root = null;
-        Count = 0;
-        comparer = customComparer;
-    }
+    public BinarySearchTree(Comparer<TKey> customComparer) => (Root, Count, comparer) = (null, 0, customComparer);
 
     /// <summary>
     ///     Gets the number nodes currently in the BST.

DataStructures/Timeline.cs

@@ -78,12 +78,7 @@ public TValue[] this[DateTime time]
         get => GetValuesByTime(time);
         set
         {
-            var overridenEvents = timeline.Where(@event => @event.Time == time).ToList();
-            foreach (var @event in overridenEvents)
-            {
-                timeline.Remove(@event);
-            }
-
+            timeline.RemoveAll(@event => @event.Time == time);
             foreach (var v in value)
             {
                 Add(time, v);