code: ///////////////////////////////////////////////////////////////////////////
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  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  Licensed under the Apache License, Version 2.0 (the "License");      //
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  //  http://www.apache.org/licenses/LICENSE-2.0                           //
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  ///////////////////////////////////////////////////////////////////////////
  
  /*
   * Open-WBO -- Copyright (c) 2013-2015, Ruben Martins, Vasco Manquinho, Ines Lynce
   * <p>
   * Permission is hereby granted, free of charge, to any person obtaining a copy of
   * this software and associated documentation files (the "Software"), to deal in
   * the Software without restriction, including without limitation the rights to
   * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
   * the Software, and to permit persons to whom the Software is furnished to do so,
   * subject to the following conditions:
   * <p>
   * The above copyright notice and this permission notice shall be included in all
   * copies or substantial portions of the Software.
   * <p>
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
   * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
   * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   */
  
  package org.logicng.solvers.maxsat.encodings;
  
  import static org.logicng.solvers.sat.MiniSatStyleSolver.mkLit;
  import static org.logicng.solvers.sat.MiniSatStyleSolver.not;
  
  import org.logicng.collections.LNGIntVector;
  import org.logicng.solvers.maxsat.algorithms.MaxSAT;
  import org.logicng.solvers.sat.MiniSatStyleSolver;
  
  /**
   * Encodes that exactly one literal from 'lits' is assigned value true.  Uses the Ladder/Regular encoding for
   * translating the AMO constraint into CNF.
   * @version 2.0.0
   * @since 1.0
   */
  public class Ladder extends Encoding {
  
      /**
       * Encodes and adds the AMO constraint to the given solver.
       * @param s    the solver
       * @param lits the literals for the constraint
       */
      public void encode(final MiniSatStyleSolver s, final LNGIntVector lits) {
          assert lits.size() != 0;
          if (lits.size() == 1) {
              addUnitClause(s, lits.get(0));
          } else {
              final LNGIntVector seqAuxiliary = new LNGIntVector();
              for (int i = 0; i < lits.size() - 1; i++) {
                  seqAuxiliary.push(mkLit(s.nVars(), false));
                  MaxSAT.newSATVariable(s);
              }
              for (int i = 0; i < lits.size(); i++) {
                  if (i == 0) {
                      addBinaryClause(s, lits.get(i), not(seqAuxiliary.get(i)));
                      addBinaryClause(s, not(lits.get(i)), seqAuxiliary.get(i));
                  } else if (i == lits.size() - 1) {
                      addBinaryClause(s, lits.get(i), seqAuxiliary.get(i - 1));
                      addBinaryClause(s, not(lits.get(i)), not(seqAuxiliary.get(i - 1)));
                  } else {
                      addBinaryClause(s, not(seqAuxiliary.get(i - 1)), seqAuxiliary.get(i));
                      addTernaryClause(s, lits.get(i), not(seqAuxiliary.get(i)), seqAuxiliary.get(i - 1));
                      addBinaryClause(s, not(lits.get(i)), seqAuxiliary.get(i));
                      addBinaryClause(s, not(lits.get(i)), not(seqAuxiliary.get(i - 1)));
                  }
              }
          }
      }
  
      @Override
      public String toString() {
          return this.getClass().getSimpleName();
      }
  }
  