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/*******************************************************************************
* Copyright (c) 2010-2012, Tamas Szabo, Istvan Rath and Daniel Varro
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*******************************************************************************/
package tools.refinery.viatra.runtime.matchers.algorithms;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import tools.refinery.viatra.runtime.matchers.util.CollectionsFactory;
/**
* Union-find data structure implementation. Note that the implementation relies on the correct implementation of the
* equals method of the type parameter's class.
*
* @author Tamas Szabo
*
* @param <V>
* the type parameter of the element's stored in the union-find data structure
*/
public class UnionFind<V> {
private final Map<V, UnionFindNodeProperty<V>> nodeMap;
final Map<V, Set<V>> setMap;
/**
* Instantiate a new union-find data structure.
*/
public UnionFind() {
nodeMap = CollectionsFactory.createMap();
setMap = CollectionsFactory.createMap();
}
/**
* Instantiate a new union-find data structure with the given elements as separate sets.
*/
public UnionFind(Iterable<V> elements) {
this();
for (V element : elements) {
makeSet(element);
}
}
/**
* Creates a new union set from a collection of elements.
*
* @param nodes
* the collection of elements
* @return the root element
*/
public V makeSet(Collection<V> nodes) {
if (!nodes.isEmpty()) {
Iterator<V> iterator = nodes.iterator();
V root = makeSet(iterator.next());
while (iterator.hasNext()) {
root = union(root, iterator.next());
}
return root;
} else {
return null;
}
}
/**
* This method creates a single set containing the given node.
*
* @param node
* the root node of the set
* @return the root element
*/
public V makeSet(V node) {
if (!nodeMap.containsKey(node)) {
UnionFindNodeProperty<V> prop = new UnionFindNodeProperty<V>(0, node);
nodeMap.put(node, prop);
Set<V> set = new HashSet<V>();
set.add(node);
setMap.put(node, set);
}
return node;
}
/**
* Find method with path compression.
*
* @param node
* the node to find
* @return the root node of the set in which the given node can be found
*/
public V find(V node) {
UnionFindNodeProperty<V> prop = nodeMap.get(node);
if (prop != null) {
if (prop.parent.equals(node)) {
return node;
} else {
prop.parent = find(prop.parent);
return prop.parent;
}
}
return null;
}
/**
* Union by rank implementation of the two sets which contain x and y; x and/or y can be a single element from the
* universe.
*
* @param x
* set or single element of the universe
* @param y
* set or single element of the universe
* @return the new root of the two sets
*/
public V union(V x, V y) {
V xRoot = find(x);
V yRoot = find(y);
if ((xRoot == null) || (yRoot == null)) {
return union( (xRoot == null) ? makeSet(x) : xRoot, (yRoot == null) ? makeSet(y) : yRoot);
}
else if (!xRoot.equals(yRoot)) {
UnionFindNodeProperty<V> xRootProp = nodeMap.get(xRoot);
UnionFindNodeProperty<V> yRootProp = nodeMap.get(yRoot);
if (xRootProp.rank < yRootProp.rank) {
xRootProp.parent = yRoot;
setMap.get(yRoot).addAll(setMap.get(xRoot));
setMap.remove(xRoot);
return yRoot;
} else {// (xRootProp.rank >= yRootProp.rank)
yRootProp.parent = xRoot;
yRootProp.rank = (xRootProp.rank == yRootProp.rank) ? yRootProp.rank + 1 : yRootProp.rank;
setMap.get(xRoot).addAll(setMap.get(yRoot));
setMap.remove(yRoot);
return xRoot;
}
} else {
return xRoot;
}
}
/**
* Places the given elements in to the same partition.
*/
public void unite(Set<V> elements) {
if (elements.size() > 1) {
V current = null;
for (V element : elements) {
if (current != null) {
if (getPartition(element) != null) {
union(current, element);
}
} else {
if (getPartition(element) != null) {
current = element;
}
}
}
}
}
/**
* Delete the set whose root is the given node.
*
* @param root
* the root node
*/
public void deleteSet(V root) {
// if (setMap.containsKey(root))
for (V n : setMap.get(root)) {
nodeMap.remove(n);
}
setMap.remove(root);
}
/**
* Returns if all given elements are in the same partition.
*/
public boolean isSameUnion(Set<V> elements) {
for (Set<V> partition : setMap.values()) {
if (partition.containsAll(elements)) {
return true;
}
}
return false;
}
/**
* Returns the partition in which the given element can be found, or null otherwise.
*/
public Set<V> getPartition(V element) {
V root = find(element);
return setMap.get(root);
}
/**
* Returns all partitions.
*/
public Collection<Set<V>> getPartitions() {
return setMap.values();
}
public Set<V> getPartitionHeads() {
return setMap.keySet();
}
}
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