001package org.cpsolver.studentsct.filter;
002
003import java.util.HashSet;
004
005import org.cpsolver.ifs.util.ToolBox;
006import org.cpsolver.studentsct.model.Student;
007
008
009/**
010 * This student filter accepts every student with the given probability. The
011 * choice for each student is remembered, i.e., if the student is passed to the
012 * filter multiple times the same answer is returned.
013 * 
014 * @author  Tomáš Müller
015 * @version StudentSct 1.3 (Student Sectioning)<br>
016 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
017 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
018 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
019 * <br>
020 *          This library is free software; you can redistribute it and/or modify
021 *          it under the terms of the GNU Lesser General Public License as
022 *          published by the Free Software Foundation; either version 3 of the
023 *          License, or (at your option) any later version. <br>
024 * <br>
025 *          This library is distributed in the hope that it will be useful, but
026 *          WITHOUT ANY WARRANTY; without even the implied warranty of
027 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
028 *          Lesser General Public License for more details. <br>
029 * <br>
030 *          You should have received a copy of the GNU Lesser General Public
031 *          License along with this library; if not see
032 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
033 */
034public class RandomStudentFilter implements StudentFilter {
035    private double iProb = 1.0;
036    private HashSet<Long> iAcceptedStudentIds = new HashSet<Long>();
037    private HashSet<Long> iRejectedStudentIds = new HashSet<Long>();
038
039    /**
040     * Constructor
041     * 
042     * @param prob
043     *            probability of acceptance of a student
044     */
045    public RandomStudentFilter(double prob) {
046        iProb = prob;
047    }
048
049    /**
050     * A student is accepted with the given probability
051     */
052    @Override
053    public boolean accept(Student student) {
054        Long studentId = Long.valueOf(student.getId());
055        if (iAcceptedStudentIds.contains(studentId))
056            return true;
057        if (iRejectedStudentIds.contains(studentId))
058            return false;
059        boolean accept = (Math.random() < iProb);
060        if (accept)
061            iAcceptedStudentIds.add(studentId);
062        else
063            iRejectedStudentIds.add(studentId);
064        return accept;
065    }
066
067    /**
068     * Set acceptance probability. Update the sets of accepted and rejected
069     * students accordingly.
070     * 
071     * @param prob
072     *            new acceptance probability
073     */
074    public void setProbability(double prob) {
075        iProb = prob;
076        int accept = (int) Math.round(prob * (iAcceptedStudentIds.size() + iRejectedStudentIds.size()));
077        while (iAcceptedStudentIds.size() < accept && !iRejectedStudentIds.isEmpty()) {
078            Long studentId = ToolBox.random(iRejectedStudentIds);
079            iRejectedStudentIds.remove(studentId);
080            iAcceptedStudentIds.add(studentId);
081        }
082        while (iAcceptedStudentIds.size() > accept && !iAcceptedStudentIds.isEmpty()) {
083            Long studentId = ToolBox.random(iAcceptedStudentIds);
084            iRejectedStudentIds.add(studentId);
085            iAcceptedStudentIds.remove(studentId);
086        }
087    }
088
089    @Override
090    public String getName() {
091        return "Random";
092    }
093
094}