@Override
	public String toString() {

		//Lorent Hugo:1,2,4,5,6;George Micheal:13,24,45,56,67;
		
		StringBuilder sb=new StringBuilder();
		Set<Entry<K, Set<Long>>> items = map.entrySet();
		for (Entry<K, Set<Long>> entry : items) {
			K key = entry.getKey();
			sb.append(key.toString());
			sb.append(':');
			boolean isFirstOne = true;
			for(Long articleId:entry.getValue()){
				if(isFirstOne)
					isFirstOne = false;
				else
					sb.append(',');
				
				sb.append(articleId);
			}
			sb.append(';');
		}
		return sb.toString();
	}