programming challenge: double words

[Ofnuts]

Mine is similar to Yoriz's, but using sets:

def double_words(word_list):
    word_set = set(word_list)
    doubles = set(''.join(pair) for pair in itertools.permutations(word_list, 2) if ''.join(pair) in word_set)
    return [word for word in word_list if word in doubles]

It works on Yoriz's word list. I ran it on the full word list I normally use. It ran quite a while and found 15,876 double words.

No time for code, but:

- build a set of all the words
- scan the llist again, and for  each word iterate x see if word[:x] is in the set, and if so if word[x:] is also in the set.

No need for the N**2 set. Complexity is O(N*L) where L is the average half-length but since it's practically a constant for large sets of random words, result must be O(N).