Data structure & java recommend

Q-2) (10 pt) Assume that we try to design a spelling checker program for a laptop computer. The spelling checker should be able to handle quickly small documents (i.e. less than O(n)). Assume that the spelling checker comes with a dictionary of about 20,000 words. a) (2pts) What data structure can be used for such a dictionary, Answer: b) (4pts) What operations must be implemented on the dictionary, Answer: c) (4pts) What is the time complexity for each operation