Question

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.

Answer 1

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.