Question

Given a node with the following structure

class Node {
int data,
Node* P1,
Node* p2;
}

We need to determine, if the node represents a Circular Doubly Link List OR a Binary Tree.
In my opinion We need to start traversing the given node in one direction

node = givenNode;
while(node->P1 != null && node->P1 != givenNode)
{
  node = node->p1
}

if(node == givenNode) // It means Circular DLL
else if(node == null)  // It means Tree

And it would take O(n) time to detect this.

Please suggest if there is any better approach than this.

Answer 1

I suggest you could check if its a doubl-linked list or not with this piece of code:

node = givenNode;
if(givenNode->P1 == null || givenNode->P2 == null)
 // It can not be double link list (circular)
else if(givenNode->p1->p2 == givenNode || givenNode->p2->p1 == givenNode)
{
//It is a double linked list
}
else
{
It is not a double linked list
}

And we have O(1) complexity