I just tried this -- you don't know _which_ combination is missing unfortunately in the case of a 2 or 3 digit number. With 3 you might be able to figure it out

I just tried this -- you don't know _which_ combination is missing unfortunately in the case of a 2 or 3 digit number. With 3 you might be able to figure it out by using the limit of 250 (e.g. if 2 4 and 7 are missing there is only 1 to recombine them and have it be less than 250), but with two how do you differentiate between say 26 and 62 in a clever, non brute force way? In case anyone wants a starting point: import random from collections import Counter rand_list = range(0, 250) random.shuffle(rand_list) missing = rand_list.pop() shuffled = ''.join([str(x) for x in rand_list]) full_list = ''.join([str(x) for x in xrange(0, 250)]) cntr = Counter() for digit in full_list: cntr[int(digit)] += 1 for digit in shuffled: cntr[int(digit)] -= 1 digits = [] for k, v in cntr.items(): for _ in range(0, v): digits.append(k)