Hey Look, This isn't a Language Shitpost

Hello /proggles/. In the midst of all of this "faggotry," I propose a thread about actual programming.

Suppose you have a sort of root directory with a large number of subdirectories all containing a large number of files. The files all exist in ranges of size from a few kilobytes to several gigabytes. Given an input file, let's conduct a quick method for searching our root directory and its subdirectories for copies of the input file.

I've thought of a fairly decent algorithm that I will share if anyone here is interested enough to share their own.

Actually, yes, let's change the problem so that the input is a list of files that must be checked.

So we have a list of k files of input of variable size that must be checked against n files, also of widely varying size for every copy that exists in that list of files. How fast can we go, /prog/?