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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="SECTION009413000000000000000">Inserting and Removing Items</A></H3>
<P>
Program <A HREF="page226.html#proghashtbl3c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page226.html#proghashtbl3c"><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> gives the code for
inserting and removing items from a <tt>ChainedHashTable</tt>.
<P>
<P><A NAME="12077"> </A><A NAME="proghashtbl3c"> </A> <IMG WIDTH=575 HEIGHT=219 ALIGN=BOTTOM ALT="program11952" SRC="img978.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img978.gif" ><BR>
<STRONG>Program:</STRONG> <tt>ChainedHashTable</tt> Class <tt>Insert</tt> and <tt>Withdraw</tt> Member Function Definitions<BR>
<P>
<P>
The implementations of the <tt>Insert</tt>
and <tt>Withdraw</tt> functions are remarkably simple.
For example,
the <tt>Insert</tt> function first calls the hash function <tt>H</tt>
to compute an array index which is used to select one of the linked lists.
The <tt>Append</tt> member function provided by the <tt>LinkedList<T></tt> class
is used to add a pointer to the object to the selected linked list.
The total running time for the <tt>Insert</tt> operation is <IMG WIDTH=130 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline62834" SRC="img979.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img979.gif" >,
where <IMG WIDTH=77 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline62836" SRC="img980.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img980.gif" > is the running time of the <tt>Object::Hash</tt> function.
Notice that if the hash function runs in constant time,
then so too does hash table insertion operation!
<P>
The <tt>Withdraw</tt> function is almost identical to the <tt>Insert</tt> function.
Instead of calling the <tt>Append</tt>,
it calls the linked list <tt>Extract</tt> function to remove the
specified object from the appropriate linked list.
The running time of <tt>Withdraw</tt> is determined by the time
of the <tt>Extract</tt> operation.
In Chapter <A HREF="page79.html#chapfds" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page79.html#chapfds"><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> this was shown to be <I>O</I>(<I>n</I>)
where <I>n</I> is the number of items in the linked list.
In the worst case, all of the items in the <tt>ChainedHashTable</tt>
have collided with each other and ended up in the same list.
I.e., in the worst case if there are <I>n</I> items in the container,
all <I>n</I> of them are in a single linked list.
In this case, the running time of the <tt>Withdraw</tt> operation
is <IMG WIDTH=132 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline62846" SRC="img981.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img981.gif" >.
<P>
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