Yesterday 's contest had some very good problems , unfortunately, it became unrated. Problem Link : https://mirror.codeforces.com/contest/1573/problem/C

The problem is based on standard topological sort Prerequisite problem .

If the cycle was found in the graph I printed -1 as the answer. else I found the topical sort of all the chapters , using cycle detection + DFS + queue.

Where I am stuck ?? After finding the topological ordering of chapters (stored in a queue a ->b->c->d.... )how do I count the number of times I will have to read the book/number of passes required ???

Please help !!!