Given a linked list. Return pointer to the node where cycle starts. If there is no cycle, return null.
Definition of a single linked list:
Implement a function detectCycle that returns a pointer to the node where cycle starts. If there is no cycle, return null.
Function detectCycle returns null because this linked list does not contain a cycle.
Function detectCycle returns pointer to the node with value 3 - the starting point of the cycle.