Check if two arrays have the same contents (in any order)

Question

I\'m using Ruby 1.8.6 with Rails 1.2.3, and need to determine whether two arrays have the same elements, regardless of whether or not they\'re in the same order. One of the

Answer 1

If you know the arrays are of equal length and neither array contains duplicates then this works too:

( array1 & array2 ) == array1

Explanation: the & operator in this case returns a copy of a1 sans any items not found in a2, which is the same as the original a1 iff both arrays have the same contents with no duplicates.

Analyis: Given that the order is unchanged, I'm guessing this is implemented as a double iteration so consistently O(n*n), notably worse for large arrays than a1.sort == a2.sort which should perform with worst-case O(n*logn).