streams/src/main/java/org/apache/kafka/streams/processor/internals/QuickUnion.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.kafka.streams.processor.internals;

import java.util.HashMap;
import java.util.NoSuchElementException;

public class QuickUnion<T> {

    private HashMap<T, T> ids = new HashMap<>();

    public void add(T id) {
        ids.put(id, id);
    }

    public boolean exists(T id) {
        return ids.containsKey(id);
    }

    public T root(T id) {
        T current = id;
        T parent = ids.get(current);

        if (parent == null)
            throw new NoSuchElementException("id: " + id.toString());

        while (!parent.equals(current)) {
            // do the path compression
            T grandparent = ids.get(parent);
            ids.put(current, grandparent);

            current = parent;
            parent = grandparent;
        }
        return current;
    }

    public void unite(T id1, T... idList) {
        for (T id2 : idList) {
            unitePair(id1, id2);
        }
    }

    private void unitePair(T id1, T id2) {
        T root1 = root(id1);
        T root2 = root(id2);

        if (!root1.equals(root2))
            ids.put(root1, root2);
    }

}