namespace WhiteRabbit { using System; using System.Collections.Generic; using System.Collections.Immutable; using System.Linq; internal sealed class StringsProcessor { public StringsProcessor(byte[] sourceString, int maxWordsCount, IEnumerable words) { var filteredSource = sourceString.Where(ch => ch != 32).ToArray(); this.NumberOfCharacters = filteredSource.Length; this.VectorsConverter = new VectorsConverter(filteredSource); // Dictionary of vectors to array of words represented by this vector var vectorsToWords = words .Where(word => word != null && word.Length > 0) .Select(word => new { word, vector = this.VectorsConverter.GetVector(word) }) .Where(tuple => tuple.vector != null) .Select(tuple => new { tuple.word, vector = tuple.vector.Value }) .GroupBy(tuple => tuple.vector) .Select(group => new { vector = group.Key, words = group.Select(tuple => tuple.word).Distinct(new ByteArrayEqualityComparer()).ToArray() }) .ToList(); this.WordsDictionary = vectorsToWords.Select(tuple => tuple.words).ToArray(); this.VectorsProcessor = new VectorsProcessor( this.VectorsConverter.GetVector(filteredSource).Value, maxWordsCount, vectorsToWords.Select(tuple => tuple.vector).ToArray()); } private VectorsConverter VectorsConverter { get; } /// /// WordsDictionary[vectorIndex] = [word1, word2, ...] /// private byte[][][] WordsDictionary { get; } private VectorsProcessor VectorsProcessor { get; } private int NumberOfCharacters { get; } #if SINGLE_THREADED public IEnumerable GeneratePhrases() #else public ParallelQuery GeneratePhrases() #endif { // 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(); // converting sequences of vectors to the sequences of words... return sums .Select(this.ConvertVectorsToWords) .SelectMany(FlattenWords) .Select(this.ConvertWordsToPhrase); } // 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 static IEnumerable> Flatten(ImmutableStack phrase) { if (phrase.IsEmpty) { return new[] { ImmutableStack.Create() }; } T[] wordVariants; var newStack = phrase.Pop(out wordVariants); return Flatten(newStack).SelectMany(remainder => wordVariants.Select(word => remainder.Push(word))); } private static IEnumerable>> FlattenWords(Tuple> wordVariants) { var item1 = wordVariants.Item1; return Flatten(wordVariants.Item2).Select(words => Tuple.Create(item1, words)); } private Tuple> ConvertVectorsToWords(int[] vectors) { var length = vectors.Length; var words = new byte[length][][]; for (var i = 0; i < length; i++) { words[i] = this.WordsDictionary[vectors[i]]; } return Tuple.Create(length, ImmutableStack.Create(words)); } private byte[] ConvertWordsToPhrase(Tuple> words) { var wordCount = words.Item1; var result = new byte[this.NumberOfCharacters + wordCount - 1]; byte[] currentWord; var currentStack = words.Item2.Pop(out currentWord); Buffer.BlockCopy(currentWord, 0, result, 0, currentWord.Length); var position = currentWord.Length; while (!currentStack.IsEmpty) { result[position] = 32; position++; currentStack = currentStack.Pop(out currentWord); Buffer.BlockCopy(currentWord, 0, result, position, currentWord.Length); position += currentWord.Length; } return result; } } }