删除Map中Value重复的记录，并且只保留Key最小的那条记录

介绍

晚上无聊的时候，我做了一个测试题，测试题的大体意思是：删除Map中Value重复的记录，并且只保留Key最小的那条记录。

例如：

I have a map with duplicate values:

("A", "1");

("B", "2");

("C", "2");

("D", "3");

("E", "3");

I would like to the map to have:

("A", "1");

("B", "2");

("D", "3");

package shuai.study.map;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;

/**
 * @author shengshu
 *
 */
public class UniqueMap {

	// Remove repetition from Map, this is core part in this Class
	public static Map<String, String> removeRepetitionFromMap(Map<String, String> map) {
		Set<Entry<String, String>> set = map.entrySet();

		List<Entry<String, String>> list = new ArrayList<Entry<String, String>>(set);

		Collections.sort(list, new Comparator<Entry<String, String>>() {
			@Override
			public int compare(Entry<String, String> entry1, Entry<String, String> entry2) {
				return Integer.valueOf(entry1.getValue().hashCode()) - Integer.valueOf(entry2.getValue().hashCode());
			}
		});

		// list.size() is dynamic change
		for (int index = 0; index < list.size(); index++) {
			String key = list.get(index).getKey();
			String value = list.get(index).getValue();

			int next_index = index + 1;

			if (next_index < list.size()) {
				String next_key = list.get(next_index).getKey();
				String next_value = list.get(next_index).getValue();

				// Remove repetition record whose key is more bigger
				if (value == next_value) {
					if (key.hashCode() < next_key.hashCode()) {
						map.remove(next_key);
						list.remove(next_index);
					} else {
						map.remove(key);
						list.remove(index);
					}

					// Due to removing repetition in List, so index will be reduced
					index--;
				}
			}
		}

		return map;
	}

	// Transfer Map to Sorted Map
	public static Map<String, String> transferToSortedMap(Map<String, String> map) {
		// Define comparator for TreeMap
		Map<String, String> new_sort_map = new TreeMap<String, String>(new Comparator<String>() {
			@Override
			public int compare(String key1, String key2) {
				return key1.hashCode() - key2.hashCode();
			}
		});

		new_sort_map.putAll(map);

		return new_sort_map;
	}

	public static void printMap(Map<String, String> map) {
		Iterator<Entry<String, String>> iterator = map.entrySet().iterator();

		while (iterator.hasNext()) {
			Entry<String, String> entry = iterator.next();

			String key = entry.getKey();
			String value = entry.getValue();

			System.out.println(key + " --> " + value);
		}
	}

	public static void main(String[] args) {
		Map<String, String> map = new HashMap<String, String>();
		map.put("A", "1");
		map.put("B", "2");
		map.put("C", "2");
		map.put("D", "3");
		map.put("E", "3");

		Map<String, String> new_map = UniqueMap.removeRepetitionFromMap(map);

		// new_sort_map is what we want
		Map<String, String> new_sort_map = UniqueMap.transferToSortedMap(new_map);

		// Print new_sort_map
		UniqueMap.printMap(new_sort_map);
	}
}

删除Map中Value重复的记录，并且只保留Key最小的那条记录