void setVal(String key, int val) {
		LinkedList node;
		if(key2node.containsKey(key)) {
			node = key2node.get(key);
			node.data = val;
			LinkedList father = node.father, son = node.son;
			if(father != null) father.son = son;
			if(son != null) son.father = father;
		} else {
			node = new LinkedList(val, key);
			if(length < bound) {
				length++;
			} else if(tail != null) {
				key2node.remove(tail.key);
				tail = tail.father;
			}
			key2node.put(key, node);
		}
		node.son = head;
		node.father = null;
		head = node;
		if(tail == null) tail = node;
	}