208. Implement Trie (Prefix Tree)

Description:

Solution:

1. We make a TrieNode() class.
2. In TrieNode(), we have two attribute: children, endOfWord
3. In insert(), if c is not in cur.children, we put the c in it. And mark the last character as endOfWord.
4. In search(), if c is not in cur.children, we return False.
5. In startsWith(), it is same with search function. But, we use prefix in this case.