Heap.java

/*******************************************************************************
* SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU Lesser General Public License Version 2.1 or later (the
* "LGPL"), in which case the provisions of the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of the LGPL, and not to allow others to use your version of
* this file under the terms of the EPL, indicate your decision by deleting
* the provisions above and replace them with the notice and other provisions
* required by the LGPL. If you do not delete the provisions above, a recipient
* may use your version of this file under the terms of the EPL or the LGPL.
* 
* Based on the original MiniSat specification from:
* 
* An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
* Sixth International Conference on Theory and Applications of Satisfiability
* Testing, LNCS 2919, pp 502-518, 2003.
*
* See www.minisat.se for the original solver in C++.
* 
*******************************************************************************/
package org.sat4j.minisat.core;

import java.io.Serializable;

import org.sat4j.core.VecInt;
import org.sat4j.specs.IVecInt;

/**
 * Heap implementation used to maintain the variables order in some heuristics.
 * 
 * @author daniel
 * 
 */
public class Heap implements Serializable {

    /*
     * default serial version id
     */
    private static final long serialVersionUID = 1L;

    private final static int left(int i) {
        return i << 1;
    }

    private final static int right(int i) {
        return (i << 1) ^ 1;
    }

    private final static int parent(int i) {
        return i >> 1;
    }

    private final boolean comp(int a, int b) {
        return activity[a] > activity[b];
    }

    private final IVecInt heap = new VecInt(); // heap of ints

    private final IVecInt indices = new VecInt(); // int -> index in heap

    private final double[] activity;

    final void percolateUp(int i) {
        int x = heap.get(i);
        while (parent(i) != 0 && comp(x, heap.get(parent(i)))) {
            heap.set(i, heap.get(parent(i)));
            indices.set(heap.get(i), i);
            i = parent(i);
        }
        heap.set(i, x);
        indices.set(x, i);
    }

    final void percolateDown(int i) {
        int x = heap.get(i);
        while (left(i) < heap.size()) {
            int child = right(i) < heap.size()
                    && comp(heap.get(right(i)), heap.get(left(i))) ? right(i)
                    : left(i);
            if (!comp(heap.get(child), x))
                break;
            heap.set(i, heap.get(child));
            indices.set(heap.get(i), i);
            i = child;
        }
        heap.set(i, x);
        indices.set(x, i);
    }

    boolean ok(int n) {
        return n >= 0 && n < indices.size();
    }

    public Heap(double[] activity) {
        // DLB findbugs ok
        this.activity = activity;
        heap.push(-1);
    }

    public void setBounds(int size) {
        assert (size >= 0);
        indices.growTo(size, 0);
    }

    public boolean inHeap(int n) {
        assert (ok(n));
        return indices.get(n) != 0;
    }

    public void increase(int n) {
        assert (ok(n));
        assert (inHeap(n));
        percolateUp(indices.get(n));
    }

    public boolean empty() {
        return heap.size() == 1;
    }

    public void insert(int n) {
        assert (ok(n));
        indices.set(n, heap.size());
        heap.push(n);
        percolateUp(indices.get(n));
    }

    public int getmin() {
        int r = heap.get(1);
        heap.set(1, heap.last());
        indices.set(heap.get(1), 1);
        indices.set(r, 0);
        heap.pop();
        if (heap.size() > 1)
            percolateDown(1);
        return r;
    }

    public boolean heapProperty() {
        return heapProperty(1);
    }

    public boolean heapProperty(int i) {
        return i >= heap.size()
                || ((parent(i) == 0 || !comp(heap.get(i), heap.get(parent(i))))
                        && heapProperty(left(i)) && heapProperty(right(i)));
    }

}