Both store strings.
When to use each? Use hash set when:
- Only need exact lookups (contains/add/remove)
- Prefix queries not needed
- Memory is limited
Use trie when:
- Need prefix queries (startsWith, autocomplete)
- Need to find all words with a prefix
- Lexicographic ordering matters
- Pattern matching with wildcards
Hash set lookup is average (hash computation), but worst case with collisions.
Trie is always . For most string lookup problems without prefix requirements, hash sets are simpler. Add prefix queries, and tries become needed.