Question

This is an interview question: Design a data structure to perform the following operation efficiently: boolean isPrefix(String s1, String s2).

I guess we can create a multimap, which maps prefixes to their strings. For instance,

strings: "aa", "ab", "abc", "ba", "ca"
multimap: "a"   -> ["aa", "ab", "abc"]
          "aa"  -> ["aa"]
          "ab"  -> ["ab", "abc"]
          "abc" -> ["abc"]
          "ba"  -> ["ba"]
          "ca"  -> ["ca"]

Which data structure would you propose ?

Answer 1

The trie data structure would seem like an obvious answer, but the problem as stated doesn’t require an advanced data structure. A simple string comparison will suffice and would be very fast. Ultimately, if you want to validate that one string is a prefix of another, you will have to compare every character at corresponding positions. No data structure eliminates the need for the character-by-character comparison.

That being said, if you’re searching for the prefix in a large body of text, there are other techniques such as Rabin-Karp probablistic string matching.