c34026b101
note: done using ```sh git grep -l "2010-2024 Google" | xargs sed -i 's/2010-2024 Google/2010-2025 Google/' ```
100 lines
3.2 KiB
Java
100 lines
3.2 KiB
Java
// Copyright 2010-2025 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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// OR-Tools solution to the N-queens problem.
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package com.google.ortools.constraintsolver.samples;
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// [START import]
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import com.google.ortools.Loader;
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import com.google.ortools.constraintsolver.DecisionBuilder;
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import com.google.ortools.constraintsolver.IntVar;
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import com.google.ortools.constraintsolver.Solver;
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// [END import]
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/** N-Queens Problem. */
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public final class NQueensCp {
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public static void main(String[] args) {
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Loader.loadNativeLibraries();
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// Instantiate the solver.
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// [START solver]
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Solver solver = new Solver("N-Queens");
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// [END solver]
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// [START variables]
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int boardSize = 8;
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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] = solver.makeIntVar(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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solver.addConstraint(solver.makeAllDifferent(queens));
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// All columns must be different because the indices of queens are all different.
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// No two queens can be on the same diagonal.
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IntVar[] diag1 = new IntVar[boardSize];
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IntVar[] diag2 = new IntVar[boardSize];
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for (int i = 0; i < boardSize; ++i) {
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diag1[i] = solver.makeSum(queens[i], i).var();
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diag2[i] = solver.makeSum(queens[i], -i).var();
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}
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solver.addConstraint(solver.makeAllDifferent(diag1));
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solver.addConstraint(solver.makeAllDifferent(diag2));
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// [END constraints]
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// [START db]
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// Create the decision builder to search for solutions.
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final DecisionBuilder db =
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solver.makePhase(queens, Solver.CHOOSE_FIRST_UNBOUND, Solver.ASSIGN_MIN_VALUE);
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// [END db]
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// [START solve]
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int solutionCount = 0;
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solver.newSearch(db);
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while (solver.nextSolution()) {
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System.out.println("Solution " + solutionCount);
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for (int i = 0; i < boardSize; ++i) {
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for (int j = 0; j < boardSize; ++j) {
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if (queens[j].value() == 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 != boardSize - 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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solver.endSearch();
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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(" failures: " + solver.failures());
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System.out.println(" branches: " + solver.branches());
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System.out.println(" wall time: " + solver.wallTime() + "ms");
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System.out.println(" Solutions found: " + solutionCount);
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// [END statistics]
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}
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private NQueensCp() {}
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}
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// [END program]
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