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.knowledgecompilation.dnnf.datastructures.dtree;
  
  import org.logicng.datastructures.Tristate;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.Literal;
  import org.logicng.formulas.Variable;
  import org.logicng.knowledgecompilation.dnnf.DnnfSatSolver;
  import org.logicng.solvers.sat.MiniSatStyleSolver;
  
  import java.util.ArrayList;
  import java.util.BitSet;
  import java.util.List;
  import java.util.SortedSet;
  
  /**
   * A leaf in a DTree.
   * @version 2.0.0
   * @since 2.0.0
   */
  public class DTreeLeaf extends DTree {
  
      protected final int id;
      protected final Formula clause;
      protected final int clauseSize;
  
      protected int[] literals;
  
      protected final BitSet separatorBitSet = new BitSet();
  
      protected DnnfSatSolver solver;
      protected final int[] staticClauseIds;
  
      /**
       * Constructs a new leaf with the given id and clause.
       * @param id     the id
       * @param clause the clause
       */
      public DTreeLeaf(final int id, final Formula clause) {
          this.id = id;
          this.clause = clause;
          this.staticClauseIds = new int[]{id};
          this.clauseSize = clause.variables().size();
          this.staticSeparator = new int[0];
          assert this.clauseSize >= 2;
      }
  
      @Override
      public void initialize(final DnnfSatSolver solver) {
          this.solver = solver;
          final SortedSet<Literal> lits = this.clause.literals();
          final int size = lits.size();
          this.staticVarSet = new BitSet();
          this.staticVariables = new int[size];
          this.literals = new int[size];
          int i = 0;
          for (final Literal literal : lits) {
              final int var = solver.variableIndex(literal);
              this.staticVarSet.set(var);
              this.staticVariables[i] = var;
              this.literals[i] = MiniSatStyleSolver.mkLit(var, !literal.phase());
              i++;
          }
      }
  
      @Override
      public int size() {
          return 1;
      }
  
      @Override
      public SortedSet<Variable> staticVariableSet() {
          return this.clause.variables();
      }
  
      @Override
      public BitSet dynamicSeparator() {
          return this.separatorBitSet;
      }
  
      @Override
      public int[] staticClauseIds() {
          return this.staticClauseIds;
      }
  
      protected boolean isSubsumed() {
          for (final int literal : this.literals) {
              if (this.solver.valueOf(literal) == Tristate.TRUE) {
                  return true;
              }
          }
          return false;
      }
  
      @Override
      public void countUnsubsumedOccurrences(final int[] occurrences) {
          if (!isSubsumed()) {
              for (final int var : this.staticVariables) {
                  final int occ = occurrences[var];
                  if (occ != -1) {
                      ++occurrences[var];
                  }
              }
          }
      }
  
      @Override
      public int depth() {
          return 1;
      }
  
      @Override
      public int widestSeparator() {
          return 0;
      }
  
      @Override
      public List<DTreeLeaf> leafs() {
          final List<DTreeLeaf> result = new ArrayList<>();
          result.add(this);
          return result;
      }
  
      /**
       * Returns the leaf's clause.
       * @return the leaf's clause
       */
      public Formula clause() {
          return this.clause;
      }
  
      @Override
      public String toString() {
          return String.format("DTreeLeaf: %d, %s", this.id, this.clause);
      }
  
      /**
       * Returns the literal integers of the clause.
       * @return literals integers of the clause
       */
      public int[] literals() {
          return this.literals;
      }
  
      /**
       * Returns the size of the leaf's clause.
       * @return the size of the leaf's clause
       */
      public int clauseSize() {
          return this.clauseSize;
      }
  
      /**
       * Returns the leaf's id.
       * @return the leaf's id
       */
      public int getId() {
          return this.id;
      }
  }
  