5 ms·

Isn't that unnecessary quadratic algorithm (nested loops, m*l iterations, instead of m + l)?

• ummonk 5y ago
  Yes, but that's the case with all the functional approaches proposed. If Python were focused on functional programming it would have a utility function for this similar to itertools.groupby (but with indices in an array instead of keys in a dictionary).
  • dragonwriter 5y ago
    > If Python were focused on functional programming it would have a utility function for this similar to itertools.groupby (but with indices in an array instead of keys in a dictionary). itertools.groupby doesn’t return a dictionary, it returns an iterator of (key, (iterator that produces values)) tuples. It sounds, though, like you want something like: from itertools import groupby def categorize_into_list(source, _range, key): first = lambda x: x[0] sublist_dict = { k: list(v[1] for v in vs) for k, vs in groupby(sorted(((key(v), v) for v in source), key=first), first)) } return [sublist_dict.get(i, []) for i in _range] Then you could do this with something like: def congruent_sets(m, l): categorize_into_list(l, m, lambda v: v % m)
    • ummonk 5y ago
      Yeah exactly.