From 792621e67fdd2f15d64402b93a30ef14d46edf02 Mon Sep 17 00:00:00 2001
From: Lucas Lemaire <zwormi@gmail.com>
Date: Wed, 7 Oct 2015 08:48:58 +0200
Subject: [PATCH] Add ShellSort with test

---
 Algorithms/Sorting/ShellSorter.cs            | 58 ++++++++++++++++++++
 MainProgram/AlgorithmsTests/ShellSortTest.cs | 32 +++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 Algorithms/Sorting/ShellSorter.cs
 create mode 100644 MainProgram/AlgorithmsTests/ShellSortTest.cs

diff --git a/Algorithms/Sorting/ShellSorter.cs b/Algorithms/Sorting/ShellSorter.cs
new file mode 100644
index 00000000..3a78dd04
--- /dev/null
+++ b/Algorithms/Sorting/ShellSorter.cs
@@ -0,0 +1,58 @@
+using System.Collections.Generic;
+using Algorithms.Common;
+
+namespace Algorithms.Sorting
+{
+    public static class ShellSorter
+    {
+        public static void BubbleSort<T>(this IList<T> collection, Comparer<T> comparer = null)
+        {
+            comparer = comparer ?? Comparer<T>.Default;
+            collection.ShellSortAscending(comparer);
+        }
+
+        /// <summary>
+        /// Public API: Sorts ascending
+        /// </summary>
+        public static void ShellSortAscending<T>(this IList<T> collection, Comparer<T> comparer)
+        {
+            bool flag = true;
+            int d = collection.Count;
+            while (flag || (d > 1))
+            {
+                flag = false;
+                d = (d + 1) / 2;
+                for (int i = 0; i < (collection.Count - d); i++)
+                {
+                    if (comparer.Compare(collection[i + d], collection[i]) < 0)
+                    {
+                        collection.Swap(i + d, i);
+                        flag = true;
+                    }
+                }
+            }
+        }
+
+        /// <summary>
+        /// Public API: Sorts descending
+        /// </summary>
+        public static void ShellSortDescending<T>(this IList<T> collection, Comparer<T> comparer)
+        {
+            bool flag = true;
+            int d = collection.Count;
+            while (flag || (d > 1))
+            {
+                flag = false;
+                d = (d + 1) / 2;
+                for (int i = 0; i < (collection.Count - d); i++)
+                {
+                    if (comparer.Compare(collection[i + d], collection[i])>0)
+                    {
+                        collection.Swap(i+d,i);
+                        flag = true;
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/MainProgram/AlgorithmsTests/ShellSortTest.cs b/MainProgram/AlgorithmsTests/ShellSortTest.cs
new file mode 100644
index 00000000..276d7a9f
--- /dev/null
+++ b/MainProgram/AlgorithmsTests/ShellSortTest.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 ShellSortTest
+    {
+        public static void DoTest()
+        {
+            DoTestAscending();
+            DoTestDescending();
+        }
+
+        public static void DoTestAscending()
+        {
+            List<int> numbers = new List<int> { 54, 26, 93, 17, 77, 31, 44, 55, 20 };
+            numbers.ShellSortAscending(Comparer<int>.Default);
+
+            Debug.Assert(numbers.SequenceEqual(numbers.OrderBy(i => i)), "Wrong SelectionSort ascending");
+        }
+
+        public static void DoTestDescending()
+        {
+            List<int> numbers = new List<int> {84,69,76,86,94,91 };
+            numbers.ShellSortDescending(Comparer<int>.Default);
+
+            Debug.Assert(numbers.SequenceEqual(numbers.OrderByDescending(i => i)), "Wrong SelectionSort descending");
+        }
+    }
+}