Interview Question: Grouping Word Anagrams (Facebook)

anagrams.py

import collections


def sort_hash(word):
    return ''.join(sorted(word))


def count_letters_hash(word):
    d = collections.defaultdict(int)
    for c in word:
        d[c] += 1
    return tuple(d.items())


def group_anagrams(words, pre_hash_function):
    result = {}
    for w in words:
        s = pre_hash_function(w.lower()) 
        if s in result:
            result[s] |= {w}
        else:
            result[s] = {w}
    return result.values()


#usage:
>>> group_anagrams(['tsar', 'rat', 'tar', 'star', 'tars', 'cheese'], sort_hash)
[set(['tars', 'tsar', 'star']), set(['cheese']), set(['rat', 'tar'])]
>>> group_anagrams(['tsar', 'rat', 'tar', 'star', 'tars', 'cheese'], count_letters_hash)
[set(['tars', 'tsar', 'star']), set(['cheese']), set(['rat', 'tar'])]