Add empty array handling to counting sort (#130)

Author: siriak

Algorithms.Tests/Sorters/Integer/CountingSorterTests.cs

@@ -8,7 +8,7 @@ namespace Algorithms.Tests.Sorters.Integer
     public static class CountingSorterTests
     {
         [Test]
-        public static void SortsArray([Random(0, 10000, 100, Distinct = true)]int n)
+        public static void SortsNonEmptyArray([Random(1, 10000, 100, Distinct = true)]int n)
         {
             // Arrange
             var sorter = new CountingSorter();
@@ -21,5 +21,12 @@ public static void SortsArray([Random(0, 10000, 100, Distinct = true)]int n)
             // Assert
             Assert.AreEqual(correctArray, testArray);
         }
+
+        [Test]
+        public static void SortsEmptyArray()
+        {
+            var sorter = new CountingSorter();
+            sorter.Sort(Array.Empty<int>());
+        }
     }
-}
+}

Algorithms/Sorters/Integer/CountingSorter.cs

@@ -25,9 +25,14 @@ public class CountingSorter : IIntegerSorter
         ///         Space complexity: O(n+k), where k is the range of the non-negative key values.
         ///     </para>
         /// </summary>
-        /// <param name="array">input array.</param>
+        /// <param name="array">Input array.</param>
         public void Sort(int[] array)
         {
+            if (array.Length == 0)
+            {
+                return;
+            }
+
             var max = array.Max();
             var min = array.Min();
             var count = new int[max - min + 1];