Why does this code get accepted on CodeChef but NOT on SPOJ?
My solution: Online Compiler and IDE - GeeksforGeeks
SPOJ: SPOJ.com - Problem PT07Y
CC: PD31 Problem - CodeChef
1 Like
SPOJ usually has stronger and trickier test cases than Codechef.
If you give this input to your code (which is valid according to constraints):
3 2
1 2
1 2
It should output NO but it gives YES. I would make a change to your DFS by considering the case when neighbor vertex is already visited (taking care of the parent of s in the DFS Tree, since those 2 nodes can’t make a cycle, I added the parameter p to be the parent of s in the DFS Tree).
if(*i == p) continue;
if(visited[*i]) return true; // Since is an edge joining two visited nodes
else Do what you have for this case
When using the former way you don’t need to check if s is visited or not before checking its neighbors 
The last change I considered is that you were reading m edges but for you m is the number of vertices.