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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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package org.optaplanner.examples.nqueens.persistence;

import java.io.File;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.List;

import org.optaplanner.examples.common.app.CommonApp;
import org.optaplanner.examples.common.app.LoggingMain;
import org.optaplanner.examples.common.persistence.AbstractSolutionImporter;
import org.optaplanner.examples.nqueens.app.NQueensApp;
import org.optaplanner.examples.nqueens.domain.Column;
import org.optaplanner.examples.nqueens.domain.NQueens;
import org.optaplanner.examples.nqueens.domain.Queen;
import org.optaplanner.examples.nqueens.domain.Row;
import org.optaplanner.persistence.common.api.domain.solution.SolutionFileIO;

public class NQueensGenerator extends LoggingMain {

    public static void main(String[] args) {
        NQueensGenerator generator = new NQueensGenerator();
        generator.writeNQueens(4);
        generator.writeNQueens(8);
        generator.writeNQueens(16);
        generator.writeNQueens(32);
        generator.writeNQueens(64);
        generator.writeNQueens(256);
    }

    protected final SolutionFileIO solutionFileIO;
    protected final File outputDir;

    public NQueensGenerator() {
        solutionFileIO = new NQueensSolutionFileIO();
        outputDir = new File(CommonApp.determineDataDir(NQueensApp.DATA_DIR_NAME), "unsolved");
    }

    public NQueensGenerator(boolean withoutDao) {
        if (!withoutDao) {
            throw new IllegalArgumentException("The parameter withoutDao (" + withoutDao + ") must be true.");
        }
        solutionFileIO = null;
        outputDir = null;
    }

    private void writeNQueens(int n) {
        String outputFileName = n + "queens.json";
        File outputFile = new File(outputDir, outputFileName);
        NQueens nQueens = createNQueens(n);
        solutionFileIO.write(nQueens, outputFile);
        logger.info("Saved: {}", outputFile);
    }

    public NQueens createNQueens(int n) {
        NQueens nQueens = new NQueens(0L);
        nQueens.setN(n);
        nQueens.setColumnList(createColumnList(nQueens));
        nQueens.setRowList(createRowList(nQueens));
        nQueens.setQueenList(createQueenList(nQueens));
        BigInteger possibleSolutionSize = BigInteger.valueOf(nQueens.getN()).pow(nQueens.getN());
        logger.info("NQueens {} has {} queens with a search space of {}.",
                n, nQueens.getN(),
                AbstractSolutionImporter.getFlooredPossibleSolutionSize(possibleSolutionSize));
        return nQueens;
    }

    private List createColumnList(NQueens nQueens) {
        int n = nQueens.getN();
        List columnList = new ArrayList<>(n);
        for (int i = 0; i < n; i++) {
            Column column = new Column(i);
            columnList.add(column);
        }
        return columnList;
    }

    private List createRowList(NQueens nQueens) {
        int n = nQueens.getN();
        List rowList = new ArrayList<>(n);
        for (int i = 0; i < n; i++) {
            Row row = new Row(i);
            rowList.add(row);
        }
        return rowList;
    }

    private List createQueenList(NQueens nQueens) {
        int n = nQueens.getN();
        List queenList = new ArrayList<>(n);
        long id = 0;
        for (Column column : nQueens.getColumnList()) {
            Queen queen = new Queen(id);
            id++;
            queen.setColumn(column);
            // Notice that we leave the PlanningVariable properties on null
            queenList.add(queen);
        }
        return queenList;
    }

}