001/*
002 * Sonar, open source software quality management tool.
003 * Copyright (C) 2008-2012 SonarSource
004 * mailto:contact AT sonarsource DOT com
005 *
006 * Sonar is free software; you can redistribute it and/or
007 * modify it under the terms of the GNU Lesser General Public
008 * License as published by the Free Software Foundation; either
009 * version 3 of the License, or (at your option) any later version.
010 *
011 * Sonar is distributed in the hope that it will be useful,
012 * but WITHOUT ANY WARRANTY; without even the implied warranty of
013 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014 * Lesser General Public License for more details.
015 *
016 * You should have received a copy of the GNU Lesser General Public
017 * License along with Sonar; if not, write to the Free Software
018 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02
019 */
020package org.sonar.graph;
021
022import java.util.*;
023
024public class MinimumFeedbackEdgeSetSolver {
025
026  private final List<FeedbackCycle> feedbackCycles;
027  private Set<FeedbackEdge> feedbackEdges;
028  private int minimumFeedbackEdgesWeight = Integer.MAX_VALUE;
029  private final int cyclesNumber;
030  private final int maxNumberCyclesForSearchingMinimumFeedback;
031  private static final int DEFAULT_MAXIMUM_NUMBER_OF_LOOPS = 1000000;
032  private static final int MAXIMUM_NUMBER_OF_CYCLE_THAT_CAN_BE_HANDLED = 1500;
033  private final int maximumNumberOfLoops;
034
035  public int getNumberOfLoops() {
036    return numberOfLoops;
037  }
038
039  private int numberOfLoops = 0;
040
041  public MinimumFeedbackEdgeSetSolver(Set<Cycle> cycles, int maxCycles) {
042    this(cycles, DEFAULT_MAXIMUM_NUMBER_OF_LOOPS, maxCycles);
043  }
044
045  public MinimumFeedbackEdgeSetSolver(Set<Cycle> cycles) {
046    this(cycles, DEFAULT_MAXIMUM_NUMBER_OF_LOOPS, MAXIMUM_NUMBER_OF_CYCLE_THAT_CAN_BE_HANDLED);
047  }
048
049  public MinimumFeedbackEdgeSetSolver(Set<Cycle> cycles, int maximumNumberOfLoops, int maxNumberCyclesForSearchingMinimumFeedback) {
050    this.maximumNumberOfLoops = maximumNumberOfLoops;
051    this.feedbackCycles = FeedbackCycle.buildFeedbackCycles(cycles);
052    this.cyclesNumber = cycles.size();
053    this.maxNumberCyclesForSearchingMinimumFeedback = maxNumberCyclesForSearchingMinimumFeedback;
054    this.run();
055  }
056
057  public int getWeightOfFeedbackEdgeSet() {
058    return minimumFeedbackEdgesWeight;
059  }
060
061  /**
062   * Get edges tagged as feedback.
063   */
064  public Set<Edge> getEdges() {
065    Set<Edge> edges = new HashSet<Edge>();
066    for (FeedbackEdge fe : feedbackEdges) {
067      edges.add(fe.getEdge());
068    }
069    return edges;
070  }
071
072  private void run() {
073    Set<FeedbackEdge> pendingFeedbackEdges = new HashSet<FeedbackEdge>();
074    if (cyclesNumber < maxNumberCyclesForSearchingMinimumFeedback) {
075      searchFeedbackEdges(0, 0, pendingFeedbackEdges);
076    }
077    else {
078      lightResearchForFeedbackEdges();
079    }
080  }
081
082  private void lightResearchForFeedbackEdges() {
083    feedbackEdges = new HashSet<FeedbackEdge>();
084    for (FeedbackCycle cycle : feedbackCycles) {
085      for (FeedbackEdge edge : cycle) {
086        feedbackEdges.add(edge);
087        break;
088      }
089    }
090    minimumFeedbackEdgesWeight = 0;
091    for(FeedbackEdge edge : feedbackEdges) {
092      minimumFeedbackEdgesWeight += edge.getWeight();
093    }
094  }
095
096  private void searchFeedbackEdges(int level, int pendingWeight, Set<FeedbackEdge> pendingFeedbackEdges) {
097    if (numberOfLoops++ > maximumNumberOfLoops) {
098      return;
099    }
100
101    if (pendingWeight >= minimumFeedbackEdgesWeight) {
102      return;
103    }
104
105    if (level == cyclesNumber) {
106      minimumFeedbackEdgesWeight = pendingWeight;
107      feedbackEdges = new HashSet<FeedbackEdge>(pendingFeedbackEdges);
108      return;
109    }
110
111    FeedbackCycle feedbackCycle = feedbackCycles.get(level);
112
113    if (doesFeedbackEdgesContainAnEdgeOfTheCycle(pendingFeedbackEdges, feedbackCycle)) {
114      searchFeedbackEdges(level + 1, pendingWeight, pendingFeedbackEdges);
115    }
116    else {
117      boolean hasAnEdgeWithOccurrenceOfOneBeenUsed = false;
118      for (FeedbackEdge feedbackEdge : feedbackCycle) {
119        if (feedbackEdge.getOccurences() == 1) {
120          if (hasAnEdgeWithOccurrenceOfOneBeenUsed) {
121            continue;
122          }
123          else {
124            hasAnEdgeWithOccurrenceOfOneBeenUsed = true;
125          }
126        }
127        int edgeWeight = addNewEdge(feedbackEdge, pendingFeedbackEdges);
128        pendingWeight += edgeWeight;
129
130        searchFeedbackEdges(level + 1, pendingWeight, pendingFeedbackEdges);
131        pendingWeight -= edgeWeight;
132        pendingFeedbackEdges.remove(feedbackEdge);
133      }
134    }
135  }
136
137  private boolean doesFeedbackEdgesContainAnEdgeOfTheCycle(Set<FeedbackEdge> pendingFeedbackEdges, FeedbackCycle cycle) {
138    boolean contains = false;
139    for (FeedbackEdge feedbackEdge : cycle) {
140      if (pendingFeedbackEdges.contains(feedbackEdge)) {
141        contains = true;
142        break;
143      }
144    }
145    return contains;
146  }
147
148  private int addNewEdge(FeedbackEdge feedbackEdge, Set<FeedbackEdge> pendingFeedbackEdges) {
149    pendingFeedbackEdges.add(feedbackEdge);
150    return feedbackEdge.getWeight();
151  }
152}