For how many vertices in a set, is top tree defined for underlying tree?

Category: QuestionsFor how many vertices in a set, is top tree defined for underlying tree?
Editor">Editor Staff asked 1 month ago

For how many vertices in a set, is top tree defined for underlying tree?
 
(a) 3
 
(b) 4
 
(c) 5
 
(d) 2
 
My enquiry is from Binary Trees in chapter Binary Trees of Data Structures & Algorithms I
 
I have been asked this question in an interview for job.

1 Answers
Editor">Editor Staff answered 1 month ago

Right answer is (d) 2
 
The best I can explain: Top tree is defined for a set having a maximum of 2 vertices for its underlying tree. Those sets having at maximum 2 vertices is called External Boundary Vertices.