How Do I Choose Between a Hash Table and a Trie (Prefix Tree)?

Question

So if I have to choose between a hash table or a prefix tree what are the discriminating factors that would lead me to choose one over the other. From my own naive point of

Answer 1

Insertion and lookup on a trie is linear with the lengh of the input string O(s).

A hash will give you a O(1) for lookup ans insertion, but first you have to calculate the hash based on the input string which again is O(s).

Conclussion, the asymptotic time complexity is linear in both cases.

The trie has some more overhead from data perspective, but you can choose a compressed trie which will put you again, more or less on a tie with the hash table.

To break the tie ask yourself this question: Do i need to lookup for full words only? Or do I need to return all words matching a prefix? (As in a predictive text input system ). For the first case, go for a hash. It is simpler and cleaner code. Easier to test and maintain. For a more ellaborated use case where prefixes or sufixes matter, go for a trie.

And if you do it just for fun, implementing a trie would put a Sunday afternoon to a good use.