The purpose of the `IsEmpty` accessor function is to determine
whether a given *N*-ary tree is the empty tree.
The implementation of this function is given in Program .
In this implementation,
the `key` pointer is zero if the tree is the empty tree.
Therefore, `IsEmpty` returns `true` if when the `key`
member variable is zero.
Clearly this is a constant time, *O*(1), operation.

**Program:** `NaryTree` Class Member Function Definitions

Copyright © 1997 by Bruno R. Preiss, P.Eng. All rights reserved.