Esmail: > oh, I forgot to mention that each list may contain duplicates.
Comparing the sorted lists is a possible O(n ln n) solution: a.sort() b.sort() a == b Another solution is to use frequency dicts, O(n): from itertools import defaultdict d1 = defaultdict(int) for el in a: d1[el] += 1 d2 = defaultdict(int) for el in b: d2[el] += 1 d1 == d2 As the arrays (Python lists) become large the second solution may become faster. Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list