[11690] | 1 | using System;
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| 2 | using System.Collections.Generic;
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| 3 | using System.Linq;
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| 4 | using System.Text;
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| 5 | using HeuristicLab.Problems.GrammaticalOptimization;
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| 6 |
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| 7 | namespace HeuristicLab.Algorithms.GrammaticalOptimization {
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| 8 | public class ExhaustiveBreadthFirstSearch {
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| 9 | public event Action<string, double> FoundNewBestSolution;
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| 10 | public event Action<string, double> SolutionEvaluated;
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| 11 |
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| 12 | private readonly int maxLen;
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| 13 | private readonly Queue<string> bfsQueue = new Queue<string>();
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| 14 |
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| 15 | public ExhaustiveBreadthFirstSearch(int maxLen) {
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| 16 | this.maxLen = maxLen;
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| 17 | }
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| 18 |
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| 19 | public void Run(IProblem problem, int maxIterations) {
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| 20 | double bestQuality = double.MinValue;
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| 21 | bfsQueue.Enqueue(problem.Grammar.SentenceSymbol.ToString());
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| 22 | var sentences = GenerateLanguage(problem.Grammar);
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| 23 | var sentenceEnumerator = sentences.GetEnumerator();
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| 24 | for (int i = 0; sentenceEnumerator.MoveNext() && i < maxIterations; i++) {
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| 25 | var sentence = sentenceEnumerator.Current;
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| 26 | var quality = problem.Evaluate(sentence);
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| 27 | RaiseSolutionEvaluated(sentence, quality);
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| 28 |
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| 29 | if (quality > bestQuality) {
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| 30 | bestQuality = quality;
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| 31 | RaiseFoundNewBestSolution(sentence, quality);
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| 32 | }
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| 33 | }
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| 34 | }
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| 35 |
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| 36 | // create sentences lazily
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| 37 | private IEnumerable<string> GenerateLanguage(IGrammar grammar) {
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| 38 | while (bfsQueue.Any()) {
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| 39 | var phrase = bfsQueue.Dequeue();
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| 40 |
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| 41 | var nt = phrase.First(grammar.IsNonTerminal);
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| 42 | var ntIdx = phrase.IndexOf(nt); // TODO perf
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| 43 | var alts = grammar.GetAlternatives(nt);
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| 44 | foreach (var alt in alts) {
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| 45 | var newPhrase = phrase.Remove(ntIdx, 1).Insert(ntIdx, alt);
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| 46 | if (newPhrase.All(grammar.IsTerminal)) {
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| 47 | yield return newPhrase;
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| 48 | } else if (grammar.MinPhraseLength(newPhrase) <= maxLen) {
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| 49 | bfsQueue.Enqueue(newPhrase);
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| 50 | }
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| 51 | }
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| 52 | }
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| 53 | }
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| 54 |
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| 55 |
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| 56 | private void RaiseSolutionEvaluated(string sentence, double quality) {
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| 57 | var handler = SolutionEvaluated;
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| 58 | if (handler != null) handler(sentence, quality);
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| 59 | }
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| 60 | private void RaiseFoundNewBestSolution(string sentence, double quality) {
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| 61 | var handler = FoundNewBestSolution;
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| 62 | if (handler != null) handler(sentence, quality);
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| 63 | }
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| 64 | }
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| 65 | }
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