org.optaplanner.examples.nqueens.solver.solution.CheatingNQueensPhaseCommand Maven / Gradle / Ivy

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OptaPlanner solves planning problems. This lightweight, embeddable planning engine implements powerful and scalable algorithms to optimize business resource scheduling and planning. This module contains the examples which demonstrate how to use it in a normal Java application.

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/*
 * Copyright 2014 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.optaplanner.examples.nqueens.solver.solution;

import java.util.List;

import org.optaplanner.core.impl.phase.custom.AbstractCustomPhaseCommand;
import org.optaplanner.core.impl.score.director.ScoreDirector;
import org.optaplanner.examples.nqueens.domain.NQueens;
import org.optaplanner.examples.nqueens.domain.Queen;
import org.optaplanner.examples.nqueens.domain.Row;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Because N Queens is not NP-complete or NP-hard, it can be cheated.
 * For this reason, N queens should not be used for benchmarking purposes.
 * 
 * This class solves any N Queens instance using a polynomial time algorithm
 * (explicit solutions algorithm).
 */
public class CheatingNQueensPhaseCommand extends AbstractCustomPhaseCommand {

    protected final transient Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    public void changeWorkingSolution(ScoreDirector scoreDirector) {
        NQueens nQueens = scoreDirector.getWorkingSolution();
        int n = nQueens.getN();
        List queenList = nQueens.getQueenList();
        List rowList = nQueens.getRowList();

        if (n % 2 != 0) {
            Queen a = queenList.get(n - 1);
            scoreDirector.beforeVariableChanged(a, "row");
            a.setRow(rowList.get(n - 1));
            scoreDirector.afterVariableChanged(a, "row");
            n--;
        }
        int halfN = n / 2;
        if (n % 6 != 2) {
            for (int i = 0; i < halfN; i++) {
                Queen a = queenList.get(i);
                scoreDirector.beforeVariableChanged(a, "row");
                a.setRow(rowList.get((2 * i) + 1));
                scoreDirector.afterVariableChanged(a, "row");

                Queen b = queenList.get(halfN + i);
                scoreDirector.beforeVariableChanged(b, "row");
                b.setRow(rowList.get(2 * i));
                scoreDirector.afterVariableChanged(b, "row");
            }
        } else {
            for (int i = 0; i < halfN; i++) {
                Queen a = queenList.get(i);
                scoreDirector.beforeVariableChanged(a, "row");
                a.setRow(rowList.get((halfN + (2 * i) - 1) % n));
                scoreDirector.afterVariableChanged(a, "row");

                Queen b = queenList.get(n - i - 1);
                scoreDirector.beforeVariableChanged(b, "row");
                b.setRow(rowList.get(n - 1 - ((halfN + (2 * i) - 1) % n)));
                scoreDirector.afterVariableChanged(b, "row");
            }
        }
        scoreDirector.triggerVariableListeners();
    }

}