Hashtable/dictionary/map lookup with regular expressions

Question

I\'m trying to figure out if there\'s a reasonably efficient way to perform a lookup in a dictionary (or a hash, or a map, or whatever your favorite language calls it) where the

Answer 1

As other respondents have pointed out, it's not possible to do this with a hash table in constant time.

One approximation that might help is to use a technique called "n-grams". Create an inverted index from n-character chunks of a word to the entire word. When given a pattern, split it into n-character chunks, and use the index to compute a scored list of matching words.

Even if you can't accept an approximation, in most cases this would still provide an accurate filtering mechanism so that you don't have to apply the regex to every key.