Implement operations for an AutoComplete feature.

1. InsertWords(words) - Given a stream of words, store the words
2. CheckPrefix(prefix) - Returns if the prefix exists
3. SearchPrefix(prefix) Given a prefix string, return words starting with the prefix string.
   Eg: Insert Words {car, cart, carpool, bus, apple, cargo}
   SearchPrefix (car) -> car, cart, carpool, cargo
   Follow up questions – SearchPrefix() return in sorted order/ top k results