ortools-clone/examples/java/NQueens.java

// Copyright 2011 Hakan Kjellerstrand hakank@gmail.com
// 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.

import java.io.*;
import java.util.*;
import java.text.*;

import com.google.ortools.constraintsolver.DecisionBuilder;
import com.google.ortools.constraintsolver.IntVar;
import com.google.ortools.constraintsolver.Solver;

public class NQueens {

    static {
        System.loadLibrary("jniortools");
    }


    /**
     *
     * Solves the N Queens problem.
     * See http://www.hakank.org/google_or_tools/nqueens2.py
     *
     */
    private static void solve(int n, int num, int print) {

        Solver solver = new Solver("NQueens");

        System.out.println("n: " + n);

        //
        // variables
        //
        IntVar[] q = solver.makeIntVarArray(n, 0, n-1, "q");

        //
        // constraints
        //
        solver.addConstraint(solver.makeAllDifferent(q));

        IntVar b = solver.makeIntVar(1, 1, "b");
        IntVar[] q1 = new IntVar[n];
        IntVar[] q2 = new IntVar[n];
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < i; j++) {
                // // q[i]+i != q[j]+j
                solver.addConstraint(
                    solver.makeNonEquality(
                         solver.makeSum(q[i],i).var(),
                         solver.makeSum(q[j],j).var()));

                // q[i]-i != q[j]-j
                solver.addConstraint(
                     solver.makeNonEquality(solver.makeSum(q[i],-i).var(),
                                            solver.makeSum(q[j],-j).var()));
            }
        }

        //
        // Solve
        //
        DecisionBuilder db = solver.makePhase(q,
                                              solver.CHOOSE_MIN_SIZE_LOWEST_MAX,
                                              solver.ASSIGN_CENTER_VALUE);
        solver.newSearch(db);
        int c = 0;
        while (solver.nextSolution()) {
            if (print != 0) {
                for(int i = 0; i < n; i++) {
                    System.out.print(q[i].value() + " ");
                }
                System.out.println();
            }
            c++;
            if (num > 0 && c >= num) {
                break;
            }
        }
        solver.endSearch();

        // Statistics
        System.out.println();
        System.out.println("Solutions: " + solver.solutions());
        System.out.println("Failures: " + solver.failures());
        System.out.println("Branches: " + solver.branches());
        System.out.println("Wall time: " + solver.wallTime() + "ms");

    }

    public static void main(String[] args) throws Exception {
        int n = 8;
        int num = 0;
        int print = 1;

        if (args.length > 0) {
            n = Integer.parseInt(args[0]);
        }

        if (args.length > 1) {
            num = Integer.parseInt(args[1]);
        }

        if (args.length > 2) {
            print = Integer.parseInt(args[2]);
        }


        NQueens.solve(n, num, print);
    }
}