code: ///////////////////////////////////////////////////////////////////////////
  //                   __                _      _   ________               //
  //                  / /   ____  ____ _(_)____/ | / / ____/               //
  //                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
  //                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
  //               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  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.                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  
  package org.logicng.testutils;
  
  import org.logicng.cardinalityconstraints.CCConfig;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.FormulaFactory;
  import org.logicng.formulas.Variable;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  
  /**
   * A generator for the n-queens problem.
   * @version 1.2
   * @since 1.2
   */
  public class NQueensGenerator {
  
      private final FormulaFactory f;
  
      public NQueensGenerator(final FormulaFactory f) {
          this.f = f;
          this.f.putConfiguration(CCConfig.builder().amoEncoding(CCConfig.AMO_ENCODER.PURE).build());
      }
  
      public Formula generate(final int n) {
          int kk = 1;
          final Variable[][] varNames = new Variable[n][];
          for (int i = 0; i < n; i++) {
              varNames[i] = new Variable[n];
              for (int j = 0; j < n; j++) {
                  varNames[i][j] = this.f.variable("v" + kk++);
              }
          }
  
          final List<Formula> operands = new ArrayList<>();
          final List<Variable> vars = new ArrayList<>();
  
          for (int i = 0; i < n; i++) {
              vars.addAll(Arrays.asList(varNames[i]).subList(0, n));
              operands.add(this.f.exo(vars).cnf());
              vars.clear();
          }
          for (int i = 0; i < n; i++) {
              for (int j = 0; j < n; j++) {
                  vars.add(varNames[j][i]);
              }
              operands.add(this.f.exo(vars).cnf());
              vars.clear();
          }
          for (int i = 0; i < n - 1; i++) {
              for (int j = 0; j < n - i; j++) {
                  vars.add(varNames[j][i + j]);
              }
              operands.add(this.f.amo(vars).cnf());
              vars.clear();
          }
          for (int i = 1; i < n - 1; i++) {
              for (int j = 0; j < n - i; j++) {
                  vars.add(varNames[j + i][j]);
              }
              operands.add(this.f.amo(vars).cnf());
              vars.clear();
          }
          for (int i = 0; i < n - 1; i++) {
              for (int j = 0; j < n - i; j++) {
                  vars.add(varNames[j][n - 1 - (i + j)]);
              }
              operands.add(this.f.amo(vars).cnf());
              vars.clear();
          }
          for (int i = 1; i < n - 1; i++) {
              for (int j = 0; j < n - i; j++) {
                  vars.add(varNames[j + i][n - 1 - j]);
              }
              operands.add(this.f.amo(vars).cnf());
              vars.clear();
          }
          return this.f.and(operands);
      }
  }
  