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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 2011 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.domain.solution;

import java.util.Comparator;

import org.optaplanner.core.impl.heuristic.selector.common.decorator.SelectionSorterWeightFactory;
import org.optaplanner.examples.nqueens.domain.NQueens;
import org.optaplanner.examples.nqueens.domain.Queen;

public class QueenDifficultyWeightFactory implements SelectionSorterWeightFactory {

    private static int calculateDistanceFromMiddle(int n, int columnIndex) {
        int middle = n / 2;
        int distanceFromMiddle = Math.abs(columnIndex - middle);
        if ((n % 2 == 0) && (columnIndex < middle)) {
            distanceFromMiddle--;
        }
        return distanceFromMiddle;
    }

    @Override
    public QueenDifficultyWeight createSorterWeight(NQueens nQueens, Queen queen) {
        int distanceFromMiddle = calculateDistanceFromMiddle(nQueens.getN(), queen.getColumnIndex());
        return new QueenDifficultyWeight(queen, distanceFromMiddle);
    }

    public static class QueenDifficultyWeight implements Comparable {

        // The more difficult queens have a lower distance to the middle
        private static final Comparator COMPARATOR = Comparator
                .comparingInt((QueenDifficultyWeight weight) -> -weight.distanceFromMiddle) // Decreasing.
                .thenComparingInt(weight -> weight.queen.getColumnIndex()); // Tie-breaker.

        private final Queen queen;
        private final int distanceFromMiddle;

        public QueenDifficultyWeight(Queen queen, int distanceFromMiddle) {
            this.queen = queen;
            this.distanceFromMiddle = distanceFromMiddle;
        }

        @Override
        public int compareTo(QueenDifficultyWeight other) {
            return COMPARATOR.compare(this, other);
        }
    }
}