I am geting WA for the SNGRAPH question. question link: https://www.codechef.com/SNCKPB17/problems/SNGRAPH
and here’s my solution: https://ideone.com/raYtCB
whenever we remove an edge from the spanning tree we need to add it back. removal of any other edge will not disconnect the graph. 
there will be some edge cases though 
Can you help me with a test case on which my code is failing. It will be very helpful. Thanks.
Refer this for solution: Editorial
Also refer answers to find sample tc which may fail your code. I hope this helps ! 