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<TITLE>Destructor and Purge Member Functions</TITLE>
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<b>Data Structures and Algorithms
with Object-Oriented Design Patterns in C++</b><br>
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<H3><A NAME="SECTION0010653000000000000000">Destructor and <tt>Purge</tt> Member Functions</A></H3>
<P>
The destructor for the <tt>BinaryTree</tt> class
is defined in Program <A HREF="page292.html#progbintree2c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page292.html#progbintree2c"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A>.
It simply calls the <tt>Purge</tt> member function to do the job.
The <tt>Purge</tt> member function is part of the <tt>Container</tt> class
interface which all container instance must provide.
The purpose of the <tt>Purge</tt> routine is to delete all the owned objects
in the container and to return the container to its initial empty state.
<P>
<P><A NAME="17416"> </A><A NAME="progbintree2c"> </A> <IMG WIDTH=575 HEIGHT=317 ALIGN=BOTTOM ALT="program17245" SRC="img1186.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1186.gif" ><BR>
<STRONG>Program:</STRONG> <tt>BinaryTree</tt> Class <tt>Purge</tt> Member Function and Destructor Definitions<BR>
<P>
<P>
Clearly the <tt>Purge</tt> function has nothing to do
if the tree is already the empty tree.
If the tree is not the empty tree,
then the <tt>Purge</tt> function has some cleaning-up to do.
It begins by deleting the root
only if the binary tree is the owner of the contained objects.
Then, because a tree always owns its subtrees,
the <tt>Purge</tt> routine deletes the left and right subtrees.
<P>
Suppose the binary tree contains <I>n</I> non-empty nodes.
Theorem <A HREF="page255.html#theoremtreesi" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page255.html#theoremtreesi"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A> tells us that there are <I>n</I>+1 empty nodes.
Altogether there are 2<I>n</I>+1=<I>O</I>(<I>n</I>) nodes.
Therefore, the running time of <tt>Purge</tt>
is <IMG WIDTH=129 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline64120" SRC="img1187.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1187.gif" > in the worst case.
<P>
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