Efficient list intersection algorithm

Question

Given two lists (not necessarily sorted), what is the most efficient non-recursive algorithm to find the set intersection of those lists?
I don't believe I have access to hashing algorithms.

Answer 1

You could put all elements of the first list into a hash set. Then, iterate the second one and, for each of its elements, check the hash to see if it exists in the first list. If so, output it as an element of the intersection.