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.pseudobooleans;
  
  import org.logicng.cardinalityconstraints.CCConfig;
  import org.logicng.cardinalityconstraints.CCEncoder;
  import org.logicng.collections.LNGIntVector;
  import org.logicng.collections.LNGVector;
  import org.logicng.configurations.ConfigurationType;
  import org.logicng.formulas.CardinalityConstraint;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.FormulaFactory;
  import org.logicng.formulas.Literal;
  import org.logicng.formulas.PBConstraint;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * An encoder for pseudo-Boolean constraints.
   * @version 2.3.0
   * @since 1.0
   */
  public class PBEncoder {
  
      protected final FormulaFactory f;
      protected final PBConfig config;
      protected final CCEncoder ccEncoder;
  
      protected PBSWC swc;
      protected PBAdderNetworks adderNetworks;
  
      /**
       * Constructs a new pseudo-Boolean encoder with given configurations.
       * @param f        the formula factory
       * @param pbConfig the pseudo-Boolean encoder configuration
       * @param ccConfig the cardinality constraints encoder configuration
       */
      public PBEncoder(final FormulaFactory f, final PBConfig pbConfig, final CCConfig ccConfig) {
          this.f = f;
          this.config = pbConfig;
          this.ccEncoder = new CCEncoder(f, ccConfig);
      }
  
      /**
       * Constructs a new pseudo-Boolean encoder with a given configuration.
       * @param f        the formula factory
       * @param pbConfig the pseudo-Boolean encoder configuration
       */
      public PBEncoder(final FormulaFactory f, final PBConfig pbConfig) {
          this.f = f;
          this.config = pbConfig;
          this.ccEncoder = new CCEncoder(f);
      }
  
      /**
       * Constructs a new pseudo-Boolean encoder which uses the configuration of the formula factory.
       * @param f the formula factory
       */
      public PBEncoder(final FormulaFactory f) {
          this.f = f;
          this.config = null;
          this.ccEncoder = new CCEncoder(f);
      }
  
      /**
       * Encodes a pseudo-Boolean constraint and returns its CNF encoding.
       * @param constraint the pseudo-Boolean constraint
       * @return the CNF encoding of the pseudo-Boolean constraint
       */
      public List<Formula> encode(final PBConstraint constraint) {
          if (constraint.isCC()) {
              return this.ccEncoder.encode((CardinalityConstraint) constraint);
          }
          final Formula normalized = constraint.normalize();
          switch (normalized.type()) {
              case TRUE:
                  return Collections.emptyList();
              case FALSE:
                  return Collections.singletonList(this.f.falsum());
              case PBC:
                  final PBConstraint pbc = (PBConstraint) normalized;
                  if (pbc.isCC()) {
                      return this.ccEncoder.encode((CardinalityConstraint) pbc);
                  }
                  return this.encode(pbc.operands(), pbc.coefficients(), pbc.rhs());
              case AND:
                  final List<Formula> list = new ArrayList<>();
                  for (final Formula op : normalized) {
                      switch (op.type()) {
                          case FALSE:
                              return Collections.singletonList(this.f.falsum());
                          case PBC:
                              list.addAll(this.encode((PBConstraint) op));
                              break;
                          default:
                              throw new IllegalArgumentException("Illegal return value of PBConstraint.normalize");
                      }
                  }
                  return Collections.unmodifiableList(list);
              default:
                  throw new IllegalArgumentException("Illegal return value of PBConstraint.normalize");
          }
      }
  
      /**
       * Returns the current configuration of this encoder.  If the encoder was constructed with a given configuration, this
       * configuration will always be used.  Otherwise, the current configuration from the formula factory is used.
       * @return the current configuration of
       */
      public PBConfig config() {
          return this.config != null ? this.config : (PBConfig) this.f.configurationFor(ConfigurationType.PB_ENCODER);
      }
  
      /**
       * Builds a pseudo Boolean constraint of the form {@code c_1 * lit_1 + c_2 * lit_2 + ... + c_n * lit_n >= k}.
       * @param lits   the literals {@code lit_1 ... lit_n}
       * @param coeffs the coefficients {@code c_1 ... c_n}
       * @param rhs    the right-hand side {@code k} of the constraint
       * @return the CNF encoding of the pseudo Boolean constraint
       * @throws IllegalArgumentException if the right-hand side of the cardinality constraint is negative or
       *                                  larger than the number of literals
       */
      protected List<Formula> encode(final Literal[] lits, final int[] coeffs, final int rhs) {
          if (rhs == Integer.MAX_VALUE) {
              throw new IllegalArgumentException("Overflow in the Encoding");
          }
          if (rhs < 0) {
              return Collections.singletonList(this.f.falsum());
          }
          final LNGVector<Literal> simplifiedLits = new LNGVector<>();
          final LNGIntVector simplifiedCoeffs = new LNGIntVector();
          final List<Formula> result = new ArrayList<>();
          if (rhs == 0) {
              for (final Literal lit : lits) {
                  result.add(lit.negate());
              }
              return result;
          }
          for (int i = 0; i < lits.length; i++) {
              if (coeffs[i] <= rhs) {
                  simplifiedLits.push(lits[i]);
                  simplifiedCoeffs.push(coeffs[i]);
              } else {
                  result.add(lits[i].negate());
              }
          }
          if (simplifiedLits.size() <= 1) {
              return result;
          }
          switch (this.config().pbEncoder) {
              case SWC:
              case BEST:
                  if (this.swc == null) {
                      this.swc = new PBSWC(this.f);
                  }
                  return this.swc.encode(simplifiedLits, simplifiedCoeffs, rhs, result);
              case BINARY_MERGE:
                  return new PBBinaryMerge(this.f, this.config()).encode(simplifiedLits, simplifiedCoeffs, rhs, result);
              case ADDER_NETWORKS:
                  if (this.adderNetworks == null) {
                      this.adderNetworks = new PBAdderNetworks(this.f);
                  }
                  return this.adderNetworks.encode(simplifiedLits, simplifiedCoeffs, rhs, result);
              default:
                  throw new IllegalStateException("Unknown pseudo-Boolean encoder: " + this.config().pbEncoder);
          }
      }
  }
  