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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.app;

import java.util.List;

import org.optaplanner.core.api.solver.Solver;
import org.optaplanner.core.api.solver.SolverFactory;
import org.optaplanner.examples.nqueens.domain.NQueens;
import org.optaplanner.examples.nqueens.domain.Queen;
import org.optaplanner.examples.nqueens.persistence.NQueensGenerator;

public class NQueensHelloWorld {

    public static void main(String[] args) {
        // Build the Solver
        SolverFactory solverFactory = SolverFactory.createFromXmlResource(
                "org/optaplanner/examples/nqueens/nqueensSolverConfig.xml");
        Solver solver = solverFactory.buildSolver();

        // Load a problem with 8 queens
        NQueens unsolved8Queens = new NQueensGenerator(true).createNQueens(8);

        // Solve the problem
        NQueens solved8Queens = solver.solve(unsolved8Queens);

        // Display the result
        System.out.println("\nSolved 8 queens:\n" + toDisplayString(solved8Queens));
    }

    public static String toDisplayString(NQueens nQueens) {
        StringBuilder displayString = new StringBuilder();
        int n = nQueens.getN();
        List queenList = nQueens.getQueenList();
        for (int row = 0; row < n; row++) {
            for (int column = 0; column < n; column++) {
                Queen queen = queenList.get(column);
                if (queen.getColumn().getIndex() != column) {
                    throw new IllegalStateException("The queenList is not in the expected order.");
                }
                displayString.append(" ");
                if (queen.getRow() != null && queen.getRow().getIndex() == row) {
                    displayString.append("Q");
                } else {
                    displayString.append("_");
                }
            }
            displayString.append("\n");
        }
        return displayString.toString();
    }

}