I'm trying to solve B — Safety Grade from SEERC 2011. My solution is to iterate over all the pair of vertices in the graph (let's call the pair (s, t)), calculate the maximum flow (using Edmond-Karp algorithm) from s to t, and the answer is the minimum value among these max flow value. Also, notice that the answer can't exceed the minimum of each vertex's degree (which won't exceed ), so each maximum flow calculation will be done in less than BFS. So, the overall complexity of the algorithm is O(n * m²).

I don't know why my solution got Runtime Error (that's the last verdict I would expect to get in this problem). I ran stress-testing for half an hour, but couldn't find any wrong test case. I need help finding what's wrong with my implementation. Thanks in advance.