Three ways quick search

Author: cschen1205

Algorithms/Algorithms.csproj

@@ -3,6 +3,7 @@
     <TargetFramework>netstandard1.4</TargetFramework>
   </PropertyGroup>
   <ItemGroup>
+    <Folder Include="DataStructures\SearchTries" />
     <Folder Include="Selection" />
   </ItemGroup>
   <ItemGroup>

Algorithms/Strings/Sort/ThreeWaysQuickSort.cs

@@ -0,0 +1,45 @@
+using System;
+using Algorithms.Utils;
+
+namespace Algorithms.Strings.Sort
+{
+    public class ThreeWaysQuickSort
+    {
+        public static void Sort(string[] a)
+        {
+            Sort(a, 0, a.Length-1, 0);
+        }
+
+        private static void Sort(string[] a, int lo, int hi, int d)
+        {
+            if (lo >= hi)
+            {
+                return;
+            }
+
+            var c = charAt(a[lo], d);
+
+            int i = lo, lt = lo, gt = hi;
+            while (i <= gt)
+            {
+                var cmp = c.CompareTo(charAt(a[i], d));
+                if(cmp > 0) SortUtil.Exchange(a, i++, lt++);
+                else if (cmp < 0) SortUtil.Exchange(a, i, gt--);
+                else i++;
+            }
+
+            Sort(a, lo, lt-1, d);
+            if(c >= 0) Sort(a, lt, gt, d+1);
+            Sort(a, gt+1, hi, d);
+        }
+
+        private static int charAt(string a, int d)
+        {
+            if (a.Length <= d)
+            {
+                return -1;
+            }
+            return a[d];
+        }
+    }
+}

AlgorithmsUnitTest/Strings/Sort/LSDUnitTest.cs

@@ -20,10 +20,9 @@ public void Test()
             var words= "bed bug dad yes zoo now for tip ilk dim tag jot sob nob sky hut men egg few jay owl joy rap gig wee was wad fee tap tar dug jam all bad yet".Split(' ');
             LSD.Sort(words);
 
-            for (var i = 0; i < words.Length; ++i)
+            for (var i = 1; i < words.Length; ++i)
             {
-                console.WriteLine(words[i]);
-                Console.WriteLine(words[i]);
+                Assert.True(words[i-1].CompareTo(words[i]) <= 0);
             }
 
         }

AlgorithmsUnitTest/Strings/Sort/MSDUnitTest.cs

@@ -20,10 +20,9 @@ public void Test()
             var words= "bed bug dad yes zoo now for tip ilk dim tag jot sob nob sky hut men egg few jay owl joy rap gig wee was wad fee tap tar dug jam all bad yet".Split(' ');
             MSD.Sort(words);
 
-            for (var i = 0; i < words.Length; ++i)
+            for (var i = 1; i < words.Length; ++i)
             {
-                console.WriteLine(words[i]);
-                Console.WriteLine(words[i]);
+                Assert.True(words[i-1].CompareTo(words[i]) <= 0);
             }
 
         }

AlgorithmsUnitTest/Strings/Sort/ThreeWaysQuickSortUnitTest.cs

@@ -0,0 +1,30 @@
+using System;
+using Algorithms.Strings.Sort;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace AlgorithmsUnitTest.Strings.Sort
+{
+    public class ThreeWaysQuickSortUnitTest
+    {
+        private ITestOutputHelper console;
+        public ThreeWaysQuickSortUnitTest(ITestOutputHelper console)
+        {
+            this.console = console;
+        }
+
+        [Fact]
+        public void Test()
+        {
+
+            var words= "bed bug dad yes zoo now for tip ilk dim tag jot sob nob sky hut men egg few jay owl joy rap gig wee was wad fee tap tar dug jam all bad yet".Split(' ');
+            ThreeWaysQuickSort.Sort(words);
+
+            for (var i = 1; i < words.Length; ++i)
+            {
+                Assert.True(words[i-1].CompareTo(words[i]) <= 0);
+            }
+
+        }
+    }
+}