/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.facebook.presto.util;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Verify.verify;
public class DisjointSet<T>
{
private static class Entry<T>
{
private T parent;
private int rank; // Without path compression, this would be equal to depth. Depth of 1-node tree is considered 0.
public Entry()
{
this(null, 0);
}
public Entry(Entry<T> entry)
{
this(entry.parent, entry.rank);
}
private Entry(T parent, int rank)
{
this.parent = parent;
this.rank = rank;
}
public T getParent()
{
return parent;
}
public void setParent(T parent)
{
this.parent = parent;
this.rank = -1;
}
public int getRank()
{
checkState(parent == null);
return rank;
}
public void incrementRank()
{
checkState(parent == null);
rank++;
}
}
private final Map<T, Entry<T>> map;
public DisjointSet()
{
map = new HashMap<>();
}
public DisjointSet(DisjointSet<T> disjointSet)
{
map = new HashMap<>(disjointSet.map);
map.replaceAll((k, v) -> new Entry<>(v));
}
/**
* @return <tt>true</tt> if the specified equivalence is new
*/
public boolean findAndUnion(T node1, T node2)
{
return union(find(node1), find(node2));
}
public T find(T element)
{
if (!map.containsKey(element)) {
map.put(element, new Entry<>());
return element;
}
return findInternal(element);
}
private boolean union(T root1, T root2)
{
if (root1.equals(root2)) {
return false;
}
Entry<T> entry1 = map.get(root1);
Entry<T> entry2 = map.get(root2);
int entry1Rank = entry1.getRank();
int entry2Rank = entry2.getRank();
verify(entry1Rank >= 0);
verify(entry2Rank >= 0);
if (entry1Rank < entry2Rank) {
// make root1 child of root2
entry1.setParent(root2);
}
else {
if (entry1Rank == entry2Rank) {
// increment rank of root1 when both side were equally deep
entry1.incrementRank();
}
// make root2 child of root1
entry2.setParent(root1);
}
return true;
}
private T findInternal(T element)
{
Entry<T> value = map.get(element);
if (value.getParent() == null) {
return element;
}
else {
T root = findInternal(value.getParent());
value.setParent(root);
return root;
}
}
public Collection<Set<T>> getEquivalentClasses()
{
// map from root element to all element in the tree
Map<T, Set<T>> rootToTreeElements = new HashMap<>();
for (Map.Entry<T, Entry<T>> entry : map.entrySet()) {
T node = entry.getKey();
T root = findInternal(node);
rootToTreeElements.computeIfAbsent(root, unused -> new HashSet<>());
rootToTreeElements.get(root).add(node);
}
return rootToTreeElements.values();
}
}