public void insert(String s) {
			Node c=root;
			for (int i=0, n=s.length(); i<n;++i) {
				int id=s.charAt(i)-'a';
				if (c.child[id]==null) {
					c.child[id]=new Node();
				}
				c=c.child[id];
			}
			c.isWord=true;
		}