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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.Row;

public class RowStrengthWeightFactory 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 RowStrengthWeight createSorterWeight(NQueens nQueens, Row row) {
        int distanceFromMiddle = calculateDistanceFromMiddle(nQueens.getN(), row.getIndex());
        return new RowStrengthWeight(row, distanceFromMiddle);
    }

    public static class RowStrengthWeight implements Comparable {

        // The stronger rows are on the side, so they have a higher distance to the middle
        private static final Comparator COMPARATOR = Comparator
                .comparingInt((RowStrengthWeight weight) -> weight.distanceFromMiddle)
                .thenComparingInt(weight -> weight.row.getIndex());

        private final Row row;
        private final int distanceFromMiddle;

        public RowStrengthWeight(Row row, int distanceFromMiddle) {
            this.row = row;
            this.distanceFromMiddle = distanceFromMiddle;
        }

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