Algorithm to tell if two arrays have identical members

Question

What\'s the best algorithm for comparing two arrays to see if they have the same members?

Assume there are no duplicates, the members can be in any order, and that n

Answer 1

The best way is probably to use hashmaps. Since insertion into a hashmap is O(1), building a hashmap from one array should take O(n). You then have n lookups, which each take O(1), so another O(n) operation. All in all, it's O(n).

In python:

def comparray(a, b): 
    sa = set(a)
    return len(sa)==len(b) and all(el in sa for el in b)