It could be. Here's a python implementation: from collections import Counter freq_to_words = {} make_freq = lambda word: tuple(sorted(dict(Counter(wor

It could be. Here's a python implementation: from collections import Counter freq_to_words = {} make_freq = lambda word: tuple(sorted(dict(Counter(word)).items())) with open('/usr/share/dict/words', 'r') as f: for line in f.read().split('\n'): freq = make_freq(line) if freq not in freq_to_words: freq_to_words[freq] = [] freq_to_words[freq].append(line) print freq_to_words[make_freq('gas')] # ['gas', 'sag'] For time complexities, this requires O(n) preprocessing but can do O(1) lookups, since it's a hash structure.