001    package net.sf.cpsolver.ifs.dbt;
002    
003    import net.sf.cpsolver.ifs.extension.Extension;
004    import net.sf.cpsolver.ifs.heuristics.VariableSelection;
005    import net.sf.cpsolver.ifs.model.Value;
006    import net.sf.cpsolver.ifs.model.Variable;
007    import net.sf.cpsolver.ifs.solution.Solution;
008    import net.sf.cpsolver.ifs.solver.Solver;
009    import net.sf.cpsolver.ifs.util.DataProperties;
010    
011    /**
012     * Selection of a variable for dynamic backtracking. <br>
013     * <br>
014     * <li>Returns null if all variables are assigned. <li>Checks if there is a
015     * varaible with all values marked as nogood (and pick it if there is any). <li>
016     * Returns the first unassigned variable. <br>
017     * <br>
018     * This IFS solver variable selection heuristics is to be used only in case of
019     * dynamic backtracking and it has no parameters.
020     * 
021     * 
022     * @version IFS 1.2 (Iterative Forward Search)<br>
023     *          Copyright (C) 2006 - 2010 Tomas Muller<br>
024     *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
025     *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
026     * <br>
027     *          This library is free software; you can redistribute it and/or modify
028     *          it under the terms of the GNU Lesser General Public License as
029     *          published by the Free Software Foundation; either version 3 of the
030     *          License, or (at your option) any later version. <br>
031     * <br>
032     *          This library is distributed in the hope that it will be useful, but
033     *          WITHOUT ANY WARRANTY; without even the implied warranty of
034     *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
035     *          Lesser General Public License for more details. <br>
036     * <br>
037     *          You should have received a copy of the GNU Lesser General Public
038     *          License along with this library; if not see
039     *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
040     */
041    public class DbtVariableSelection<V extends Variable<V, T>, T extends Value<V, T>> implements VariableSelection<V, T> {
042        private DbtPropagation<V, T> iProp = null;
043    
044        public DbtVariableSelection(DataProperties properties) {
045        }
046    
047        /**
048         * Heuristics initialization
049         * 
050         * @see VariableSelection#init(Solver)
051         */
052        @Override
053        public void init(Solver<V, T> solver) {
054            for (Extension<V, T> extension : solver.getExtensions()) {
055                if (extension instanceof DbtPropagation<?, ?>) {
056                    iProp = (DbtPropagation<V, T>) extension;
057                }
058            }
059        }
060    
061        /**
062         * Variable selection
063         * 
064         * @see VariableSelection#selectVariable(Solution)
065         */
066        @Override
067        public V selectVariable(Solution<V, T> solution) {
068            if (solution.getModel().nrUnassignedVariables() == 0) {
069                return null;
070            }
071            if (iProp != null) {
072                for (V variable : solution.getModel().unassignedVariables()) {
073                    if (iProp.goodValues(variable).isEmpty()) {
074                        return variable;
075                    }
076                }
077            }
078            return solution.getModel().unassignedVariables().iterator().next();
079        }
080    
081    }