Implement a trie with insert, search, and startsWith methods.
Note:
You may assume that all inputs are consist of lowercase letters a-z.
http://dongxicheng.org/structure/trietree/
[LeetCode] Implement Trie (Prefix Tree) 实现字典树(前缀树)
原文：http://www.cnblogs.com/grandyang/p/4491665.html