org.chocosolver.graphsolver.cstrs.symmbreaking.PropGirth Maven / Gradle / Ivy

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A graph module for Choco Solver.
There is a newer version: 4.2.2
package org.chocosolver.graphsolver.cstrs.symmbreaking;

import org.chocosolver.graphsolver.variables.IUndirectedGraphVar;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.Variable;
import org.chocosolver.util.ESat;

import java.util.HashSet;

/**
 * @author Моклев Вячеслав
 */
public class PropGirth extends Propagator {

	private IUndirectedGraphVar graph;
	private int n;
	private IntVar girth;

	public PropGirth(IUndirectedGraphVar graphVar, IntVar girth) {
		super(new Variable[] {girth, graphVar}, PropagatorPriority.LINEAR, false);
		graph = graphVar;
		n = graphVar.getNbMaxNodes();
		this.girth = girth;
	}

	@Override
	public void propagate(int evtmask) throws ContradictionException {
		int upperGraphGirth = getUpperGraphGirth();
		int lowerGraphGirth = getLowerGraphGirth();
		if (upperGraphGirth < girth.getUB()) {
			girth.updateUpperBound(upperGraphGirth, this);
		}
		if (upperGraphGirth < girth.getLB()) {
			throw new ContradictionException();
		}
		if (lowerGraphGirth > girth.getLB()) {
			girth.updateLowerBound(lowerGraphGirth, this);
		}
		if (lowerGraphGirth > girth.getUB()) {
			throw new ContradictionException();
		}
	}

	@Override
	public ESat isEntailed() {
		int upperGraphGirth = getUpperGraphGirth();
		int lowerGraphGirth = getLowerGraphGirth();
		if (upperGraphGirth < girth.getLB()) {
			return ESat.FALSE;
		}
		if (lowerGraphGirth > girth.getUB()) {
			return ESat.FALSE;
		}
		if (graph.isInstantiated() && girth.isInstantiatedTo(lowerGraphGirth)) {
			return ESat.TRUE;
		}
		return ESat.UNDEFINED;
	}

	private int getUpperGraphGirth() {
		int g = n + 1;
		for (int i = 0; i < n; i++) {
			int pg = getUpperGraphGirth(i);
			if (pg < g) {
				g = pg;
			}
		}
		return g;
	}

	private int getLowerGraphGirth() {
		int g = n + 1;
		for (int i = 0; i < n; i++) {
			int pg = getLowerGraphGirth(i);
			if (pg < g) {
				g = pg;
			}
		}
		return g;
	}

	private int getUpperGraphGirth(int vertex) {
		HashSet> reachable = new HashSet<>();
		reachable.add(new Pair<>(vertex, -1));
		for (int i = 1; i <= n; i++) {
			HashSet> set = new HashSet<>();
			for (Pair u: reachable) {
				for (int v: graph.getMandNeighOf(u.getA())) {
					if (v != u.getB()) {
						if (v == vertex) {
							return i;
						}
						set.add(new Pair<>(v, u.getA()));
					}
				}
			}
			reachable = set;
		}
		return n + 1;
	}

	private int getLowerGraphGirth(int vertex) {
		HashSet> reachable = new HashSet<>();
		reachable.add(new Pair<>(vertex, -1));
		for (int i = 1; i <= n; i++) {
			HashSet> set = new HashSet<>();
			for (Pair u: reachable) {
				for (int v: graph.getPotNeighOf(u.getA())) {
					if (v != u.getB()) {
						if (v == vertex) {
							return i;
						}
						set.add(new Pair<>(v, u.getA()));
					}
				}
			}
			reachable = set;
		}
		return n + 1;
	}
}