Code cleanup

WhiteRabbit/PrecomputedPermutationsGenerator.cs

@@ -0,0 +1,37 @@
+namespace WhiteRabbit
+{
+    using System.Collections.Generic;
+    using System.Linq;
+
+    internal class PrecomputedPermutationsGenerator
+    {
+        private static PermutationsGenerator.Permutation[] Permutations1 { get; } = PermutationsGenerator.HamiltonianPermutations(1).ToArray();
+
+        private static PermutationsGenerator.Permutation[] Permutations2 { get; } = PermutationsGenerator.HamiltonianPermutations(2).ToArray();
+
+        private static PermutationsGenerator.Permutation[] Permutations3 { get; } = PermutationsGenerator.HamiltonianPermutations(3).ToArray();
+
+        private static PermutationsGenerator.Permutation[] Permutations4 { get; } = PermutationsGenerator.HamiltonianPermutations(4).ToArray();
+
+        private static PermutationsGenerator.Permutation[] Permutations5 { get; } = PermutationsGenerator.HamiltonianPermutations(5).ToArray();
+
+        public static IEnumerable<PermutationsGenerator.Permutation> HamiltonianPermutations(int n)
+        {
+            switch(n)
+            {
+                case 1:
+                    return Permutations1;
+                case 2:
+                    return Permutations2;
+                case 3:
+                    return Permutations3;
+                case 4:
+                    return Permutations4;
+                case 5:
+                    return Permutations5;
+                default:
+                    return PermutationsGenerator.HamiltonianPermutations(n);
+            }
+        }
+    }
+}

WhiteRabbit/Program.cs

@@ -3,6 +3,7 @@
     using System;
     using System.Collections.Generic;
     using System.Linq;
+    using System.Numerics;
     using System.Security.Cryptography;
     using System.Text;
 
@@ -16,20 +17,43 @@
         /// </summary>
         public static void Main()
         {
-            var processor = new StringsProcessor("poultry outwits ants", 3);
-            foreach (var phrase in processor.GeneratePhrases(ReadInput()))
+            var processor = new StringsProcessor("poultry outwits ants", 4);
+            var expectedHashes = new[]
             {
-                var hash = GetHash(phrase);
-                Console.WriteLine(hash + ": " + phrase);
+                "e4820b45d2277f3844eac66c903e84be",
+                "23170acc097c24edb98fc5488ab033fe",
+                "665e5bcb0c20062fe8abaaf4628bb154",
+            };
+
+            var expectedHashesAsVectors = new HashSet<Vector<byte>>(expectedHashes.Select(hash => new Vector<byte>(StringToByteArray(hash))));
+
+            foreach (var result in AddHashes(processor.GeneratePhrases(ReadInput())))
+            {
+                if (expectedHashesAsVectors.Contains(result.Item2))
+                {
+                    Console.WriteLine("Found phrase: " + result.Item1);
+                }
             }
         }
 
-        private static string GetHash(string input)
+        // Code taken from http://stackoverflow.com/a/321404/831314
+        private static byte[] StringToByteArray(string hex)
+        {
+            return Enumerable.Range(0, hex.Length)
+                             .Where(x => x % 2 == 0)
+                             .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
+                             .ToArray();
+        }
+
+        private static IEnumerable<Tuple<string, Vector<byte>>> AddHashes(IEnumerable<string> input)
         {
             using (MD5 hasher = MD5.Create())
             {
-                var data = hasher.ComputeHash(Encoding.UTF8.GetBytes(input));
-                return string.Concat(data.Select(b => b.ToString("x2")));
+                foreach (var line in input)
+                {
+                    var data = hasher.ComputeHash(Encoding.ASCII.GetBytes(line));
+                    yield return Tuple.Create(line, new Vector<byte>(data));
+                }
             }
         }
 

WhiteRabbit/StringsProcessor.cs

@@ -22,6 +22,7 @@
 
         public IEnumerable<string> GeneratePhrases(IEnumerable<string> words)
         {
+            // Dictionary of vectors to array of words represented by this vector
             var formattedWords = words
                 .Distinct()
                 .Select(word => new { word, vector = this.VectorsConverter.GetVector(word) })
@@ -30,9 +31,10 @@
                 .GroupBy(tuple => tuple.vector)
                 .ToDictionary(group => group.Key, group => group.Select(tuple => tuple.word).ToArray());
 
+            // task of finding anagrams could be reduced to the task of finding sequences of dictionary vectors with the target sum
+            var sums = this.VectorsProcessor.GenerateSequences(formattedWords.Keys);
 
-            var sums = this.VectorsProcessor.GenerateSums(formattedWords.Keys);
-
+            // converting sequences of vectors to the sequences of words...
             var anagramsWords = sums
                 .Select(sum => ImmutableStack.Create(sum.Select(vector => formattedWords[vector]).ToArray()))
                 .SelectMany(Flatten)
@@ -41,14 +43,15 @@
             return anagramsWords.Select(list => string.Join(" ", list));
         }
 
-        private IEnumerable<ImmutableStack<string>> Flatten(ImmutableStack<string[]> phrase)
+        // Converts e.g. pair of variants [[a, b, c], [d, e]] into all possible pairs: [[a, d], [a, e], [b, d], [b, e], [c, d], [c, e]]
+        private IEnumerable<ImmutableStack<T>> Flatten<T>(ImmutableStack<T[]> phrase)
         {
             if (phrase.IsEmpty)
             {
-                return new[] { ImmutableStack.Create<string>() };
+                return new[] { ImmutableStack.Create<T>() };
             }
 
-            string[] wordVariants;
+            T[] wordVariants;
             var newStack = phrase.Pop(out wordVariants);
             return Flatten(newStack).SelectMany(remainder => wordVariants.Select(word => remainder.Push(word)));
         }

WhiteRabbit/VectorsConverter.cs

@@ -4,6 +4,10 @@
     using System.Linq;
     using System.Numerics;
 
+    /// <summary>
+    /// Converts strings to vectors containing chars count, based on a source string.
+    /// E.g. for source string "abc", string "a" is converted to [1, 0, 0], while string "bcb" is converted to [0, 2, 1].
+    /// </summary>
     internal class VectorsConverter
     {
         public VectorsConverter(string sourceString)

WhiteRabbit/VectorsProcessor.cs

@@ -32,14 +32,16 @@
 
         private long Iterations { get; set; } = 0;
 
-        public IEnumerable<Vector<byte>[]> GenerateSums(IEnumerable<Vector<byte>> vectors)
+
+        // Produces all sequences of vectors with the target sum
+        public IEnumerable<Vector<byte>[]> GenerateSequences(IEnumerable<Vector<byte>> vectors)
         {
             var filteredVectors = FilterVectors(vectors);
             var dictionary = ImmutableStack.Create(filteredVectors.ToArray());
-            var orderedSums = GenerateOrderedSums(this.Target, ImmutableStack.Create<Vector<byte>>(), dictionary);
-            var allSums = orderedSums.SelectMany(GeneratePermutations);
+            var unorderedSequences = GenerateUnorderedSequences(this.Target, ImmutableStack.Create<Vector<byte>>(), dictionary);
+            var allSequences = unorderedSequences.SelectMany(GeneratePermutations);
 
-            return allSums;
+            return allSequences;
         }
 
         private IEnumerable<Vector<byte>> FilterVectors(IEnumerable<Vector<byte>> vectors)
@@ -58,8 +60,11 @@
             }
         }
 
-        // This method takes most of the time, so everything related to it must be optimized
-        private IEnumerable<Vector<byte>[]> GenerateOrderedSums(Vector<byte> remainder, ImmutableStack<Vector<byte>> partialSumStack, ImmutableStack<Vector<byte>> dictionaryStack)
+        // This method takes most of the time, so everything related to it must be optimized.
+        // In every sequence, next vector always goes after the previous one from dictionary.
+        // E.g. if dictionary is [x, y, z], then only [x, y] sequence could be generated, and [y, x] will never be generated.
+        // That way, the complexity of search goes down by a factor of MaxVectorsCount! (as if [x, y] does not add up to a required target, there is no point in checking [y, x])
+        private IEnumerable<Vector<byte>[]> GenerateUnorderedSequences(Vector<byte> remainder, ImmutableStack<Vector<byte>> partialSumStack, ImmutableStack<Vector<byte>> dictionaryStack)
         {
             var count = partialSumStack.Count() + 1;
             if (count < this.MaxVectorsCount)
@@ -79,7 +84,7 @@
                     }
                     else if ((newRemainder & Negative) == Vector<byte>.Zero)
                     {
-                        foreach (var result in GenerateOrderedSums(newRemainder, partialSumStack.Push(currentVector), dictionaryTail))
+                        foreach (var result in GenerateUnorderedSequences(newRemainder, partialSumStack.Push(currentVector), dictionaryTail))
                         {
                             yield return result;
                         }
@@ -109,7 +114,7 @@
 
         private IEnumerable<T[]> GeneratePermutations<T>(T[] original)
         {
-            foreach (var permutation in PermutationsGenerator.HamiltonianPermutations(original.Length))
+            foreach (var permutation in PrecomputedPermutationsGenerator.HamiltonianPermutations(original.Length))
             {
                 yield return permutation.Select(i => original[i]).ToArray();
             }

WhiteRabbit/WhiteRabbit.csproj

@@ -53,6 +53,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="PrecomputedPermutationsGenerator.cs" />
     <Compile Include="PermutationsGenerator.cs" />
     <Compile Include="StringsProcessor.cs" />
     <Compile Include="Program.cs" />