Time complexity to insert a node before the node pointed by some pointer in circular singly list of n nodes?

Question

I think that it is O(N) because in a circular singly list the pointer visits n nodes so that node to be inserted precedes the current node.

Have I got it right?

Answer 1

The usual traversal and insertion would take O(N) time. However, it can be done in O(1) as well, if the nodes can be modified.
Let the list look like A -> B-> C -> D -> A , we are given a pointer to C , and we have to insert E . Now, create a copy of C and insert it after C itself. The list now looks like A -> B-> C -> C(copy) -> D -> A . Now, we can modify the values of the original C node to store the values of E node, so the list now becomes A -> B-> E -> C -> D -> A . Since you've only created a node and inserted it in place, it takes O(1) time complexity.