120 lines
3.8 KiB
Java
120 lines
3.8 KiB
Java
// Copyright 2010-2024 Google LLC
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// [START program]
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package com.google.ortools.sat.samples;
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// [START import]
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import com.google.ortools.Loader;
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import com.google.ortools.sat.CpModel;
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import com.google.ortools.sat.CpSolver;
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import com.google.ortools.sat.CpSolverSolutionCallback;
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import com.google.ortools.sat.CpSolverStatus;
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import com.google.ortools.sat.IntVar;
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import com.google.ortools.sat.LinearExpr;
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// [END import]
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/** OR-Tools solution to the N-queens problem. */
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public final class NQueensSat {
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// [START solution_printer]
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static class SolutionPrinter extends CpSolverSolutionCallback {
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public SolutionPrinter(IntVar[] queensIn) {
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solutionCount = 0;
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queens = queensIn;
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}
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@Override
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public void onSolutionCallback() {
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System.out.println("Solution " + solutionCount);
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for (int i = 0; i < queens.length; ++i) {
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for (int j = 0; j < queens.length; ++j) {
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if (value(queens[j]) == i) {
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System.out.print("Q");
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} else {
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System.out.print("_");
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}
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if (j != queens.length - 1) {
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System.out.print(" ");
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}
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}
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System.out.println();
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}
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solutionCount++;
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}
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public int getSolutionCount() {
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return solutionCount;
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}
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private int solutionCount;
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private final IntVar[] queens;
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}
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// [END solution_printer]
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public static void main(String[] args) {
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Loader.loadNativeLibraries();
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// Create the model.
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// [START model]
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CpModel model = new CpModel();
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// [END model]
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// [START variables]
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int boardSize = 8;
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// There are `BoardSize` number of variables, one for a queen in each column of the board. The
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// value of each variable is the row that the queen is in.
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IntVar[] queens = new IntVar[boardSize];
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for (int i = 0; i < boardSize; ++i) {
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queens[i] = model.newIntVar(0, boardSize - 1, "x" + i);
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}
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// [END variables]
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// Define constraints.
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// [START constraints]
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// All rows must be different.
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model.addAllDifferent(queens);
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// No two queens can be on the same diagonal.
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LinearExpr[] diag1 = new LinearExpr[boardSize];
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LinearExpr[] diag2 = new LinearExpr[boardSize];
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for (int i = 0; i < boardSize; ++i) {
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diag1[i] = LinearExpr.newBuilder().add(queens[i]).add(i).build();
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diag2[i] = LinearExpr.newBuilder().add(queens[i]).add(-i).build();
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}
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model.addAllDifferent(diag1);
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model.addAllDifferent(diag2);
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// [END constraints]
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// Create a solver and solve the model.
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// [START solve]
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CpSolver solver = new CpSolver();
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SolutionPrinter cb = new SolutionPrinter(queens);
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// Tell the solver to enumerate all solutions.
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solver.getParameters().setEnumerateAllSolutions(true);
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// And solve.
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CpSolverStatus unusedStatus = solver.solve(model, cb);
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// [END solve]
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// Statistics.
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// [START statistics]
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System.out.println("Statistics");
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System.out.println(" conflicts : " + solver.numConflicts());
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System.out.println(" branches : " + solver.numBranches());
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System.out.println(" wall time : " + solver.wallTime() + " s");
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System.out.println(" solutions : " + cb.getSolutionCount());
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// [END statistics]
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}
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private NQueensSat() {}
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}
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// [END program]
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