Hy guys....

I need your suggestions for implementing an efficient data structure in android app.

I am developing a dictionary game (word game) in which user make a word and system will check either this word exist in dictionary or not. i placed that  dictionary in raw folder(.txt file). No deletion or insertion operations can be performed just tell user either word is exist or not.
I am confused on these questions...

1.which data structure is best solution to response user  at 0(1).? 
2.Is it necessary to make a database and when app is launched system load words from that .txt file into array and perform searching.

I will highly appreciate your suggestions.