互いに素セット構造

package com.gxu.dawnlab_algorithm5;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Stack;

/**
 * 并查集结构
 * @author junbin
 *
 * 2019年7月7日
 */
public class UnionFind {
	public static class Element<V> {
		public V value;
		public Element(V value){
			this.value = value;
		}
	}

	public static class UnionFindSet<V> {
		public HashMap<V, Element<V>> elementMap;
		public HashMap<Element<V>, Element<V>> fatherMap;
		public HashMap<Element<V>, Integer> rankMap;

		public UnionFindSet(List<V> list) {
			elementMap = new HashMap<V, Element<V>>();
			fatherMap = new HashMap<Element<V>, Element<V>>();
			rankMap = new HashMap<Element<V>, Integer>();
			for(V value : list){
				Element<V> element = new Element<V>(value);
				elementMap.put(value, element);
				fatherMap.put(element, element);
				rankMap.put(element, 1);
			}
		}

		private Element<V> findHead(Element<V> element) {
			Stack<Element<V>> path = new Stack<Element<V>>();
			while(element != fatherMap.get(element)){
				path.push(element);
				element = fatherMap.get(element);
			}
			while(!path.isEmpty()){
				fatherMap.put(path.pop(), element);
			}
			
			return element;
		}
		
		public boolean isSameSet(V a, V b) {
			return findHead(elementMap.get(a)) == findHead(elementMap.get(b));
		}

		public void union(V a, V b) {
			if (elementMap.containsKey(a) && elementMap.containsKey(b)) {
				Element<V> aF = findHead(elementMap.get(a));
				Element<V> bF = findHead(elementMap.get(b));
				if(aF != bF){
					Element<V> big = rankMap.get(aF) >= rankMap.get(bF) ? aF : bF;
					Element<V> small = big == aF ? bF : aF;
					fatherMap.put(small, big);
					rankMap.put(big, rankMap.get(aF) + rankMap.get(bF));
					rankMap.remove(small);
				}
			}
		}
		
		public static void main(String[] args) {
			List<String> list = new ArrayList<String>();
			list.add("a");
			list.add("b");
			list.add("c");
			list.add("d");
			list.add("e");
			list.add("f");
			list.add("g");
			UnionFindSet<String> union = new UnionFindSet<String>(list);
			System.out.println(union.isSameSet("a", "b"));
			union.union("a", "b");
		}

	}

}

「プログラマーコード面接ガイド」P476の詳細を参照してください。