The third example - common contacts in a social network

Social networks are transforming our society and the way people relate to each other. Facebook, LinkedIn, Twitter, and Instagram have millions of users who use these networks to share life moments with their friends, make new professional contacts, promote their professional brand, meet new people, or simply know the latest trends in the world.

We can see a social network as a graph where users are the nodes of the graph and relations between users are the arcs of the graph. As occurs with graphs, there are social networks such as Facebook, where relations between users are undirected or bidirectional. If a user A is connected with user B, the user B is connected with A too. On the contrary, there are social networks such as Twitter where relations between users are directed. We say in this case that user A follows user B, but the contrary is not necessarily true.

In this section, we are going to implement an algorithm to calculate the...