Good algorithm and data structure for looking up words with missing letters?

Question

so I need to write an efficient algorithm for looking up words with missing letters in a dictionary and I want the set of possible words.

For example, if I have th??

Answer 1

Build a hash set of all the words. To find matches, replace the question marks in the pattern with each possible combination of letters. If there are two question marks, a query consists of 26² = 676 quick, constant-expected-time hash table lookups.

import itertools

words = set(open("/usr/share/dict/words").read().split())

def query(pattern):
    i = pattern.index('?')
    j = pattern.rindex('?') + 1
    for combo in itertools.product('abcdefghijklmnopqrstuvwxyz', repeat=j-i):
        attempt = pattern[:i] + ''.join(combo) + pattern[j:]
        if attempt in words:
            print attempt

This uses less memory than my other answer, but it gets exponentially slower as you add more question marks.

Answer 2

Have you considered using a Ternary Search Tree? The lookup speed is comparable to a trie, but it is more space-efficient.

I have implemented this data structure several times, and it is a quite straightforward task in most languages.