Implement knuth morris pratt

Author: cschen1205

cs-algorithms-unit-tests/Strings/Search/BoyerMooreUnitTest.cs

@@ -0,0 +1,42 @@
+using System;
+using Algorithms.Strings.Search;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace AlgorithmsUnitTest.Strings.Search
+{
+    public class BoyerMooreUnitTest
+    {
+
+        private ITestOutputHelper console;
+
+        public BoyerMooreUnitTest(ITestOutputHelper console)
+        {
+            this.console = console;
+        }
+
+        [Fact]
+        public void Test()
+        {
+            String text = "o fare thee well, poor devil of a Sub-Sub, whose commen- \n" + "tator I am. Thou belongest to that hopeless, sallow tribe \n"
+                          + "which no wine of this world will ever warm ; and for whom \n" + "even Pale Sherry would be too rosy-strong ; but with whom \n"
+                          + "one sometimes loves to sit, and feel poor-devilish, too ; and \n"
+                          + "grow convivial upon tears ; and say to them bluntly with full \n" + "eyes and empty glasses, and in not altogether unpleasant \n"
+                          + "sadness Give it up, Sub-Subs ! For by how much the more \n" + "pains ye take to please the world, by so much the more shall \n"
+                          + "ye forever go thankless ! Would that I could clear out \n" + "Hampton Court and the Tuileries for ye ! But gulp down \n"
+                          + "your tears and hie aloft to the royal-mast with your hearts ; \n" + "for your friends who have gone before are clearing out the \n"
+                          + "seven-storied heavens, and making refugees of long-pampered \n" + "Gabriel, Michael, and Raphael, against your coming. Here \n"
+                          + "ye strike but splintered hearts together there, ye shall \n" + "strike unsplinterable glasses! ";
+
+            BoyerMoore bm = new BoyerMoore("the");
+            print("found at " + bm.Search(text));
+            Assert.NotEqual(-1, bm.Search(text));
+        }
+
+        private void print(String content)
+        {
+            Console.WriteLine(content);
+            console.WriteLine(content);
+        }
+    }
+}

cs-algorithms/Strings/Search/BoyerMoore.cs

@@ -21,19 +21,19 @@ public BoyerMoore(string pat)
 
         public int Search(string text)
         {
-            int skip = 1;
+            int skip;
             for (int i = 0; i < text.Length - M; i+=skip)
             {
-                var j;
-                for (j = M - 1; j >= 0; j--)
+                skip = 0;
+                for (var j = M - 1; j >= 0; j--)
                 {
                     if (text[i + j] != pat[j])
                     {
                         skip = Math.Max(1, j - right[text[i + j]]);
                         break;
                     }
                 }
-                if (j == -1) return i;
+                if (skip == 0) return i;
             }
             return -1;
         }

cs-algorithms/Strings/Search/KnuthMorrisPratt.cs

@@ -0,0 +1,41 @@
+namespace Algorithms.Strings.Search
+{
+    public class KnuthMorrisPratt
+    {
+        private const int R = 256;
+        private int M;
+        private int[][] dfs;
+        public KnuthMorrisPratt(string pat)
+        {
+            M = pat.Length;
+            dfs = new int[R][];
+            for (var i = 0; i < R; ++i)
+            {
+                dfs[i] = new int[M];
+            }
+            dfs[0][0] = 1;
+            int X = 0;
+            for (var i = 1; i < M; ++i)
+            {
+                for (var r = 0; r < R; ++i)
+                {
+                    dfs[r][i] = dfs[r][X];
+                }
+                dfs[pat[i]][i] = i + 1;
+                X = dfs[pat[i]][X];
+            }
+        }
+
+        public int Search(string text)
+        {
+            int N = text.Length;
+            int X = 0;
+            for (var i = 0; i < N; ++i)
+            {
+                X = dfs[text[i]][X];
+                if (X == M) return i;
+            }
+            return -1;
+        }
+    }
+}