Pergunta de entrevista da empresa InterviewBit

First there were some basic maths questions which were very confusing from the interviewer's end. Then there was a tree + disjoint set union problem which was medium level. Finally when I solved the tree problem, the interviewer asked me a problem which was so tough that on codeforces (where the problem was taken from), only around 20 people in the whole world were able to answer it during contest.