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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="SECTION0015231000000000000000">Depth-First Solver</A></H3>
<P>
This section presents a backtracking solver
that finds the best solution to a given problem by
performing depth-first traversal of the solution space.
Program <A HREF="page450.html#progsolution3h" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page450.html#progsolution3h"><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> declares the concrete <tt>DepthFirstSolver</tt> class.
This <tt>DepthFirstSolver</tt> class simply provides an implementation
for the <tt>DoSolve</tt> routine.
<P>
<P><A NAME="33611"> </A><A NAME="progsolution3h"> </A> <IMG WIDTH=575 HEIGHT=85 ALIGN=BOTTOM ALT="program32715" SRC="img1839.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1839.gif" ><BR>
<STRONG>Program:</STRONG> <tt>DepthFirstSolver</tt> Class Definition<BR>
<P>
<P>
The <tt>DoSolve</tt> routine for the <tt>DepthFirstSolver</tt> class
is given in Program <A HREF="page450.html#progsolution2c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page450.html#progsolution2c"><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>.
Clearly, this routine simply does a complete,
depth-first traversal of the solution space.<A NAME="tex2html861" HREF="footnode.html#33614" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/footnode.html#33614"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/foot_motif.gif"></A>
Note that the implementation does not depend upon
the characteristics of the problem being solved.
In this sense the solver is a generic, <em>abstract solver</em>
and can be used to solve any problem that has a tree-structured solution space!
<P>
<P><A NAME="33615"> </A><A NAME="progsolution2c"> </A> <IMG WIDTH=575 HEIGHT=315 ALIGN=BOTTOM ALT="program32731" SRC="img1840.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1840.gif" ><BR>
<STRONG>Program:</STRONG> <tt>DepthFirstSolver</tt> Class <tt>DoSolve</tt> Member Function Definition<BR>
<P>
<P>
Since the <tt>DoSolve</tt> routine in Program <A HREF="page450.html#progsolution2c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page450.html#progsolution2c"><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>
visits all the nodes in the solution space,
it is essentially a <em>brute-force</em> algorithm.
And because the recursive routine backs up
and then tries different alternatives,
it is called a <em>backtracking</em> algorithm.
<P>
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