Getting a run error in one test case

#1

In my code all the test cases are being passed and in one test case it is showing run error.Please help what me with the issue.

#2

The code is https://ide.codingblocks.com/s/613986

#3

check for this testcas
3 4 5 6
and 6 connected to 4

now cycle is detected in this case so check =1 you break at node3 both slow and fast is at node 3

and then before below loop you again point slow to head(3)
now you move slow but slow->next will never we equal to head and you stuck in loop

#4

Modified code