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<b>Data Structures and Algorithms
with Object-Oriented Design Patterns in C++</b><br>
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<H2><A NAME="SECTION005270000000000000000"><tt>Prepend</tt></A></H2>
<P>
To <em>prepend</em><A NAME=3625> </A> an element to a linked list
is to insert that element in front of the first element of the list.
The prepended list element becomes the new head of the list.
Program <A HREF="page95.html#proglinklist5c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page95.html#proglinklist5c"><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 algorithm for the
<tt>Prepend</tt> member function of the <tt>LinkedList<T></tt> class.
<P>
<P><A NAME="3838"> </A><A NAME="proglinklist5c"> </A> <IMG WIDTH=575 HEIGHT=161 ALIGN=BOTTOM ALT="program3629" SRC="img626.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img626.gif" ><BR>
<STRONG>Program:</STRONG> <tt>LinkedList<T></tt> Class <tt>Prepend</tt> Function Definition<BR>
<P>
<P>
The <tt>Prepend</tt> function first allocates a new <tt>ListElement<T></tt>.
Its <tt>datum</tt> field is initialized with the value to be prepended
to the list, <tt>item</tt>; and
the <tt>next</tt> field is made to point to the
first element of the existing list by initializing it with
the value of the current <tt>head</tt> pointer.
If the list is initially empty,
both <tt>head</tt> and <tt>tail</tt> are made to point at the new element.
Otherwise, just <tt>head</tt> needs to be updated.
<P>
Note, <tt>operator new</tt> calls the constructor for objects of
class <tt>ListElement<T></tt>.
In Section <A HREF="page90.html#secfdslistelem" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page90.html#secfdslistelem"><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> the running time of the constructor
was determined to be <IMG WIDTH=124 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline61025" SRC="img621.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img621.gif" >.
And since the body of the <tt>Prepend</tt> function adds
only a constant amount of work,
the running time of the <tt>Prepend</tt> function is also <IMG WIDTH=124 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline61025" SRC="img621.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img621.gif" >.
If <tt>T</tt> is one of the built-in types,
then its copy constructor does a constant amount of work,
and the running time of <tt>Prepend</tt> simplifies to <I>O</I>(1).
<P>
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