Add PigeonHole sort algorithm with test

lucaghersi · Oct 7, 2015 · 96ee270 · 96ee270
1 parent 81f9a0c
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diff --git a/Algorithms/Sorting/PigeonHoleSorter.cs b/Algorithms/Sorting/PigeonHoleSorter.cs
@@ -0,0 +1,61 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Algorithms.Sorting
+{
+    /// <summary>
+    /// Only support IList<int> Sort
+    /// Also called CountSort (not CountingSort)
+    /// </summary>
+    public static class PigeonHoleSorter
+    {
+        public static void PigeonHoleSort(this IList<int> collection)
+        {
+            collection.PigeonHoleSortAscending();
+        }
+
+        public static void PigeonHoleSortAscending(this IList<int> collection)
+        {
+            int min = collection.Min();
+            int max = collection.Max();
+            int size = max - min + 1;
+            int[] holes = new int[size];
+            foreach (int x in collection)
+            {
+                holes[x - min]++;
+            }
+
+            int i = 0;
+            for (int count = 0; count < size; count++)
+            {
+                while (holes[count]-- > 0)
+                {
+                    collection[i] = count + min;
+                    i++;
+                }
+            }    
+        }
+
+        public static void PigeonHoleSortDescending(this IList<int> collection)
+        {
+            int min = collection.Min();
+            int max = collection.Max();
+            int size = max - min + 1;
+            int[] holes = new int[size];
+            foreach (int x in collection)
+            {
+                holes[x - min]++;
+            }
+
+            int i = 0;
+            for (int count = size-1; count >= 0; count--)
+            {
+                while (holes[count]-- >0)
+                {
+                    collection[i] = count + min;
+                    i++;
+                }
+            }
+        }
+    }
+}
diff --git a/MainProgram/AlgorithmsTests/PigeonHoleSortTest.cs b/MainProgram/AlgorithmsTests/PigeonHoleSortTest.cs
@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using Algorithms.Sorting;
+
+namespace C_Sharp_Algorithms.AlgorithmsTests
+{
+    public static class PigeonHoleSortTest
+    {
+        public static void DoTest()
+        {
+            DoTestAscending();
+            DoTestDescending();
+        }
+
+        public static void DoTestAscending()
+        {
+            List<int> numbers = new List<int> { 23, 42, 4, 16, 8, 15, 3, 9, 55, 0, 34, 12, 2, 46, 25 };
+            numbers.PigeonHoleSortAscending();
+
+            Debug.Assert(numbers.SequenceEqual(numbers.OrderBy(i => i)), "Wrong PigeonHole ascending");
+        }
+
+        public static void DoTestDescending()
+        {
+            List<int> numbers = new List<int> { 23, 42, 4, 16, 8, 15, 3, 9, 55, 0, 34, 12, 2, 46, 25 };
+            numbers.PigeonHoleSortDescending();
+
+            Debug.Assert(numbers.SequenceEqual(numbers.OrderByDescending(i => i)), "Wrong PigeonHole descending");
+        }
+    }
+}