Multiset.java

import java.util.HashMap;

/* @author: jaswant developer.jaswant@gmail.com
 * @algorithm: hashing
 * @use: holding frequency map, similar to multiset in c++
*/
class MultiSet<K> {

	private HashMap<K, Integer> multiSet = new HashMap<K, Integer>();
	private int size;

	public int get(K key){
		return multiSet.getOrDefault(key, 0);
	}

	public void add(K key){
		size++;
		multiSet.put(key, get(key)+ 1);
	}

	public void remove(K key){
		int freq = get(key);
		size--;
		if(freq == 1){
			multiSet.remove(key);
		}else{
			multiSet.put(key, freq - 1);
		}
	}
	
	public int size(){
		return size;
	}

	public boolean isEmpty(){
		return size == 0;
	}

	public boolean containsKey(K key){
		return multiSet.containsKey(key);
	}
	
	@Override
	public String toString(){
		return multiSet.toString();
	}
}