001package net.sf.cpsolver.studentsct.filter; 002 003import java.util.HashSet; 004 005import net.sf.cpsolver.ifs.util.ToolBox; 006import net.sf.cpsolver.studentsct.model.Student; 007 008/** 009 * This student filter accepts every student with the given probability. The 010 * choice for each student is remembered, i.e., if the student is passed to the 011 * filter multiple times the same answer is returned. 012 * 013 * @version StudentSct 1.2 (Student Sectioning)<br> 014 * Copyright (C) 2007 - 2010 Tomáš Müller<br> 015 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br> 016 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br> 017 * <br> 018 * This library is free software; you can redistribute it and/or modify 019 * it under the terms of the GNU Lesser General Public License as 020 * published by the Free Software Foundation; either version 3 of the 021 * License, or (at your option) any later version. <br> 022 * <br> 023 * This library is distributed in the hope that it will be useful, but 024 * WITHOUT ANY WARRANTY; without even the implied warranty of 025 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 026 * Lesser General Public License for more details. <br> 027 * <br> 028 * You should have received a copy of the GNU Lesser General Public 029 * License along with this library; if not see 030 * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>. 031 */ 032public class RandomStudentFilter implements StudentFilter { 033 private double iProb = 1.0; 034 private HashSet<Long> iAcceptedStudentIds = new HashSet<Long>(); 035 private HashSet<Long> iRejectedStudentIds = new HashSet<Long>(); 036 037 /** 038 * Constructor 039 * 040 * @param prob 041 * probability of acceptance of a student 042 */ 043 public RandomStudentFilter(double prob) { 044 iProb = prob; 045 } 046 047 /** 048 * A student is accepted with the given probability 049 */ 050 @Override 051 public boolean accept(Student student) { 052 Long studentId = new Long(student.getId()); 053 if (iAcceptedStudentIds.contains(studentId)) 054 return true; 055 if (iRejectedStudentIds.contains(studentId)) 056 return false; 057 boolean accept = (Math.random() < iProb); 058 if (accept) 059 iAcceptedStudentIds.add(studentId); 060 else 061 iRejectedStudentIds.add(studentId); 062 return accept; 063 } 064 065 /** 066 * Set acceptance probability. Update the sets of accepted and rejected 067 * students accordingly. 068 * 069 * @param prob 070 * new acceptance probability 071 */ 072 public void setProbability(double prob) { 073 iProb = prob; 074 int accept = (int) Math.round(prob * (iAcceptedStudentIds.size() + iRejectedStudentIds.size())); 075 while (iAcceptedStudentIds.size() < accept && !iRejectedStudentIds.isEmpty()) { 076 Long studentId = ToolBox.random(iRejectedStudentIds); 077 iRejectedStudentIds.remove(studentId); 078 iAcceptedStudentIds.add(studentId); 079 } 080 while (iAcceptedStudentIds.size() > accept && !iAcceptedStudentIds.isEmpty()) { 081 Long studentId = ToolBox.random(iAcceptedStudentIds); 082 iRejectedStudentIds.add(studentId); 083 iAcceptedStudentIds.remove(studentId); 084 } 085 } 086 087}