content: /**
   * Copyright (c) 2017-2018, the Alpha Team.
   * All rights reserved.
   *
   * Additional changes made by Siemens.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   * 1) Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   *
   * 2) Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package at.ac.tuwien.kr.alpha.core.solver.heuristics;
  
  import at.ac.tuwien.kr.alpha.core.common.Assignment;
  import at.ac.tuwien.kr.alpha.core.common.NoGood;
  import at.ac.tuwien.kr.alpha.core.solver.ChoiceManager;
  
  import static at.ac.tuwien.kr.alpha.core.programs.atoms.Literals.atomOf;
  
  import java.util.Deque;
  import java.util.LinkedList;
  import java.util.Random;
  
  /**
   * A BerkMin-like heuristics that uses activity of literals and a fixed-size queue instead of a stack of NoGoods.
   * Copyright (c) 2017-2018, the Alpha Team.
   */
  public class BerkMinLiteral extends BerkMin {
  
  	private Deque<Integer> activeLiterals = new LinkedList<>();
  	private static final int DEFAULT_QUEUE_SIZE = 32;
  	private final int queueSize;
  
  	BerkMinLiteral(Assignment assignment, ChoiceManager choiceManager, int decayPeriod, double decayFactor, Random random, int queueSize) {
  		super(assignment, choiceManager, decayPeriod, decayFactor, random);
  		this.queueSize = queueSize;
  	}
  
  	BerkMinLiteral(Assignment assignment, ChoiceManager choiceManager, Random random) {
  		this(assignment, choiceManager, DEFAULT_DECAY_PERIOD, DEFAULT_DECAY_FACTOR, random, DEFAULT_QUEUE_SIZE);
  	}
  
  	@Override
  	public int chooseAtom() {
  		return  getMostActiveChoosableAtom(activeLiterals.stream());
  	}
  
  	private void pushToStack(Integer literal) {
  		if (choiceManager.isAtomChoice(atomOf(literal))) {
  			activeLiterals.addFirst(literal);
  			// Restrict the size of the queue.
  			if (activeLiterals.size() > queueSize) {
  				activeLiterals.removeLast();
  			}
  		}
  	}
  
  	@Override
  	protected void pushToStack(NoGood noGood) {
  		if (noGood != null) {
  			for (Integer literal : noGood) {
  				pushToStack(literal);
  			}
  		}
  	}
  }
  