What is the algorithm for "familiar through so many people"?

Question

Social media

Hello. There are materials that describe how the algorithms implemented in some social projects work. When they show a connection with a certain person through "friends-friends-friends".
Thank you.

Answer 1

Social connections is a graph, it can be oriented, depending on the situation. The situation "know through 5 people" is, the very first thing that came to mind, the shortest path in an undirected graph corresponding to a directed link graph. And algorithms for finding such a path are classics.

Answer 2

conventional depth-first search