[abnewusers]

I have been asked to implement such question:

Given a data file like csv, two columns in it, each line contains “calling No, called No”. Each line actually represents a phone conversion by two person. If A talks to B, and C talks to B, then A and B are friends, A and C are acquaintances. I am asked to look for the person who has the most acquaintances.

[xpi0t0s]

Seems easy enough. Where are you stuck? Do you understand the requirements?
Have you tried doing it on paper to get an idea of what algorithm you might use?