/**
* Copyright (c) 1999-2014, Ecole des Mines de Nantes
* All rights reserved.
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* 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
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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;
import java.util.Random;
/**
* Random heuristic
*
* @since 01/01/2014
* @author Jean-Guillaume Fages
*/
public class Rk implements F{
//***********************************************************************************
// VARIABLES
//***********************************************************************************
public static int DEFAULT_K = 30;
protected UndirectedGraph graph;
protected int n, k, iter;
protected BitSet out, inMIS;
protected Random rd;
//***********************************************************************************
// CONSTRUCTORS
//***********************************************************************************
/**
* Creates an instance of the Random heuristic to compute independent sets on graph
* @param graph on which IS have to be computed
* @param k number of iterations (i.e. number of expected IS per propagation)
*/
public Rk(UndirectedGraph graph, int k){
this.graph = graph;
this.k = k;
n = graph.getNbMaxNodes();
out = new BitSet(n);
inMIS = new BitSet(n);
rd = new Random(0);
}
/**
* Creates an instance of the Random heuristic to compute independent sets on graph
* uses the default setting DEFAULT_K=30
* @param graph on which IS have to be computed
*/
public Rk(UndirectedGraph graph){
this(graph,DEFAULT_K);
}
//***********************************************************************************
// METHODS
//***********************************************************************************
@Override
public void prepare() {
iter = 0;
}
@Override
public void computeMIS() {
iter++;
out.clear();
inMIS.clear();
while (out.cardinality() < n) {
int nb = rd.nextInt(n - out.cardinality());
int idx = out.nextClearBit(0);
for (int i = idx; i >= 0 && i < n && nb >= 0; i = out.nextClearBit(i + 1)) {
idx = i;
nb--;
}
inMIS.set(idx);
out.set(idx);
ISet nei = graph.getNeighOf(idx);
for (int j = nei.getFirstElement(); j >= 0; j = nei.getNextElement()) {
out.set(j);
}
}
}
//***********************************************************************************
// ACCESSORS
//***********************************************************************************
@Override
public BitSet getMIS(){
return inMIS;
}
@Override
public boolean hasNextMIS(){
return iter<k;
}
}