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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="SECTION0017412000000000000000">Data Structures for Dijkstra's Algorithm</A></H3>
<P>
The implementation of Dijkstra's algorithm described below
uses the <tt>TableEntry</tt> structure declared in Program&nbsp;<A HREF="page567.html#proggraphalgs1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page567.html#proggraphalgs1c"><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>.
Each <tt>TableEntry</tt> instance has three fields,
<tt>known</tt>, <tt>distance</tt> and <tt>predecessor</tt>,
which correspond to the variables
 <IMG WIDTH=12 HEIGHT=24 ALIGN=MIDDLE ALT="tex2html_wrap_inline72349" SRC="img2456.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2456.gif"  >,  <IMG WIDTH=14 HEIGHT=24 ALIGN=MIDDLE ALT="tex2html_wrap_inline72351" SRC="img2457.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2457.gif"  > and  <IMG WIDTH=14 HEIGHT=14 ALIGN=MIDDLE ALT="tex2html_wrap_inline72353" SRC="img2458.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2458.gif"  >, respectively.
<P>
<P><A NAME="52058">&#160;</A><A NAME="proggraphalgs1c">&#160;</A> <IMG WIDTH=575 HEIGHT=353 ALIGN=BOTTOM ALT="program52055" SRC="img2478.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2478.gif"  ><BR>
<STRONG>Program:</STRONG> Data Structures for Dijkstra's Algorithm<BR>
<P>
<P>
In each pass of its operation,
Dijkstra's algorithm selects from the set of vertices
for which the shortest-path is not yet known
the one with the smallest tentative distance.
Therefore, we use a <em>priority queue</em>
to represent this set of vertices.
<P>
The priority assigned to a vertex is its tentative distance.
The class <tt>Assoc</tt> defined in Program&nbsp;<A HREF="page567.html#proggraphalgs1c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page567.html#proggraphalgs1c"><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>
is used to associate of a priority with a given object instance.
The <tt>Assoc</tt> class is derived from
the <tt>Association</tt> class given in Section&nbsp;<A HREF="page125.html#secadtsassociations" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page125.html#secadtsassociations"><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>.
Notice that the <tt>Assoc</tt> constructor calls <tt>RescindOwnership</tt>
to prevent the destructor from deleting the associated object instance.
<P>
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