Linked Lists and Sentinal node

Question

So i have been asked in my homework to merge-sort 2 different sorted circular linked lists without useing a sentinal node allso the lists can be empty, my questsion is what is a sentinal node in the first place?

Answer 1

a sentinal node is a node that contains no real data - it's just there for the convenience of the implementation.

Thus a list with 4 real elements might have one or more extra nodes, making a total of 5 or 6 nodes.

Those extra nodes might be place holders (e.g. marking where you started the merge), pseudo-nodes indicating the head of the list, or anything else the algorithm designer can think up.

Answer 2

A sentinel node is a node that you add to your code to avoid handling degeneracies with special code. For merge sort for example, you can add a node with value = INFINITY to the end of both lists that you want to merge, this guarantees that once you hit the end of a list you can't go beyond that because the value is always greater (or equal) to the values in the other list.

So if you are not using a sentinel, you have to write code to handle this. In your merge routine, you should check that you've reached the end..

Answer 3

Sentinel node is a traversal path terminator in linked lists and tree. It doesn't hold or reference any data managed by the data structure. One of the benefit is to Reduce algorithmic complexity and code size.In your case the complexity,code size will be increased and speed of operation will be decreased.