/**
* Copyright (c) 1999-2014, Ecole des Mines de Nantes
* All rights reserved.
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * 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.
* * Neither the name of the Ecole des Mines de Nantes nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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*/
package solver.constraints.nary.nValue.amnv.mis;
import util.objects.graphs.UndirectedGraph;
import util.objects.setDataStructures.ISet;
import java.util.BitSet;
/**
* Min Degree heuristic
*
* @since 01/01/2014
* @author Jean-Guillaume Fages
*/
public class MD implements F{
//***********************************************************************************
// VARIABLES
//***********************************************************************************
protected UndirectedGraph graph;
protected int n;
protected BitSet out, inMIS;
protected int[] nbNeighbours, fifo;
//***********************************************************************************
// CONSTRUCTORS
//***********************************************************************************
/**
* Creates an instance of the Min Degree heuristic to compute independent sets on graph
* @param graph
*/
public MD(UndirectedGraph graph){
this.graph = graph;
n = graph.getNbMaxNodes();
out = new BitSet(n);
inMIS = new BitSet(n);
nbNeighbours = new int[n];
fifo = new int[n];
}
//***********************************************************************************
// METHODS
//***********************************************************************************
@Override
public void prepare() {}
@Override
public void computeMIS() {
out.clear();
inMIS.clear();
for (int i = 0; i < n; i++) {
nbNeighbours[i] = graph.getNeighOf(i).getSize();
}
int idx = out.nextClearBit(0);
while (idx < n) {
for (int i = out.nextClearBit(idx + 1); i < n; i = out.nextClearBit(i + 1)) {
if (nbNeighbours[i] < nbNeighbours[idx]) {
idx = i;
}
}
addToMIS(idx);
idx = out.nextClearBit(0);
}
}
protected void addToMIS(int node) {
ISet nei = graph.getNeighOf(node);
inMIS.set(node);
out.set(node);
int sizeFifo=0;
for (int j = nei.getFirstElement(); j >= 0; j = nei.getNextElement()) {
if (!out.get(j)) {
out.set(j);
fifo[sizeFifo++] = j;
}
}
for (int i=0; i<sizeFifo; i++) {
nei = graph.getNeighOf(fifo[i]);
for (int j = nei.getFirstElement(); j >= 0; j = nei.getNextElement()) {
nbNeighbours[j]--;
}
}
}
//***********************************************************************************
// ACCESSORS
//***********************************************************************************
@Override
public BitSet getMIS(){
return inMIS;
}
@Override
public boolean hasNextMIS(){
return false;
}
}