php array_intersect() efficiency

Question

consider the below script. two arrays with only three values.when i compare these two arrays using array_intersect(). the result is fast.

Answer 1

Intersection can be implemented by constructing a set of the searched values in the second array, and looking up in a set can be made so fast that it takes essentially constant time on average. Therefore, the runtime of the whole algorithm can be in O(n).

Alternatively, one can sort the second array (in O(n log n)). Since looking up in a sorted array has a runtime in O(log n), the whole algorithm should then have a runtime in O(n log n).

According to a (short, unscientific) test I just ran, this seems to be the case for php's array_intersect:

Here's the code I used to test it. As you can see, for an input size as small as 1000, you don't need to worry.