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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="algorithm.Searching"></a><a class="link" href="Searching.html" title="Searching Algorithms">Searching Algorithms</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore">Boyer-Moore
Search</a></span></dt>
<dt><span class="section"><a href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool">Boyer-Moore-Horspool
Search</a></span></dt>
<dt><span class="section"><a href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt">Knuth-Morris-Pratt
Search</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="the_boost_algorithm_library.Searching.BoyerMoore"></a><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore" title="Boyer-Moore Search">Boyer-Moore
Search</a>
</h3></div></div></div>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h0"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.overview"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.overview">Overview</a>
</h5>
<p>
The header file 'boyer_moore.hpp' contains an implementation of the Boyer-Moore
algorithm for searching sequences of values.
</p>
<p>
The Boyer–Moore string search algorithm is a particularly efficient string
searching algorithm, and it has been the standard benchmark for the practical
string search literature. The Boyer-Moore algorithm was invented by Bob Boyer
and J. Strother Moore, and published in the October 1977 issue of the Communications
of the ACM , and a copy of that article is available at <a href="http://www.cs.utexas.edu/~moore/publications/fstrpos.pdf" target="_top">http://www.cs.utexas.edu/~moore/publications/fstrpos.pdf</a>.
</p>
<p>
The Boyer-Moore algorithm uses two precomputed tables to give better performance
than a naive search. These tables depend on the pattern being searched for,
and give the Boyer-Moore algorithm larger a memory footprint and startup
costs than a simpler algorithm, but these costs are recovered quickly during
the searching process, especially if the pattern is longer than a few elements.
</p>
<p>
However, the Boyer-Moore algorithm cannot be used with comparison predicates
like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">search</span></code>.
</p>
<p>
Nomenclature: I refer to the sequence being searched for as the "pattern",
and the sequence being searched in as the "corpus".
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h1"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.interface"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.interface">Interface</a>
</h5>
<p>
For flexibility, the Boyer-Moore algorithm has two interfaces; an object-based
interface and a procedural one. The object-based interface builds the tables
in the constructor, and uses operator () to perform the search. The procedural
interface builds the table and does the search all in one step. If you are
going to be searching for the same pattern in multiple corpora, then you
should use the object interface, and only build the tables once.
</p>
<p>
Here is the object interface:
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">patIter</span><span class="special">></span>
<span class="keyword">class</span> <span class="identifier">boyer_moore</span> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">boyer_moore</span> <span class="special">(</span> <span class="identifier">patIter</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">patIter</span> <span class="identifier">last</span> <span class="special">);</span>
<span class="special">~</span><span class="identifier">boyer_moore</span> <span class="special">();</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">corpusIter</span><span class="special">></span>
<span class="identifier">corpusIter</span> <span class="keyword">operator</span> <span class="special">()</span> <span class="special">(</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_first</span><span class="special">,</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_last</span> <span class="special">);</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
and here is the corresponding procedural interface:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">patIter</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">corpusIter</span><span class="special">></span>
<span class="identifier">corpusIter</span> <span class="identifier">boyer_moore_search</span> <span class="special">(</span>
<span class="identifier">corpusIter</span> <span class="identifier">corpus_first</span><span class="special">,</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_last</span><span class="special">,</span>
<span class="identifier">patIter</span> <span class="identifier">pat_first</span><span class="special">,</span> <span class="identifier">patIter</span> <span class="identifier">pat_last</span> <span class="special">);</span>
</pre>
<p>
</p>
<p>
Each of the functions is passed two pairs of iterators. The first two define
the corpus and the second two define the pattern. Note that the two pairs
need not be of the same type, but they do need to "point" at the
same type. In other words, <code class="computeroutput"><span class="identifier">patIter</span><span class="special">::</span><span class="identifier">value_type</span></code>
and <code class="computeroutput"><span class="identifier">curpusIter</span><span class="special">::</span><span class="identifier">value_type</span></code> need to be the same type.
</p>
<p>
The return value of the function is an iterator pointing to the start of
the pattern in the corpus. If the pattern is not found, it returns the end
of the corpus (<code class="computeroutput"><span class="identifier">corpus_last</span></code>).
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h2"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.performance"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.performance">Performance</a>
</h5>
<p>
The execution time of the Boyer-Moore algorithm, while still linear in the
size of the string being searched, can have a significantly lower constant
factor than many other search algorithms: it doesn't need to check every
character of the string to be searched, but rather skips over some of them.
Generally the algorithm gets faster as the pattern being searched for becomes
longer. Its efficiency derives from the fact that with each unsuccessful
attempt to find a match between the search string and the text it is searching,
it uses the information gained from that attempt to rule out as many positions
of the text as possible where the string cannot match.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h3"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.memory_use"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.memory_use">Memory
Use</a>
</h5>
<p>
The algorithm allocates two internal tables. The first one is proportional
to the length of the pattern; the second one has one entry for each member
of the "alphabet" in the pattern. For (8-bit) character types,
this table contains 256 entries.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h4"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.complexity"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.complexity">Complexity</a>
</h5>
<p>
The worst-case performance to find a pattern in the corpus is <span class="emphasis"><em>O(N)</em></span>
(linear) time; that is, proportional to the length of the corpus being searched.
In general, the search is sub-linear; not every entry in the corpus need
be checked.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h5"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.exception_safety"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.exception_safety">Exception
Safety</a>
</h5>
<p>
Both the object-oriented and procedural versions of the Boyer-Moore algorithm
take their parameters by value and do not use any information other than
what is passed in. Therefore, both interfaces provide the strong exception
guarantee.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h6"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.notes"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.notes">Notes</a>
</h5>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
When using the object-based interface, the pattern must remain unchanged
for during the searches; i.e, from the time the object is constructed
until the final call to operator () returns.
</li>
<li class="listitem">
The Boyer-Moore algorithm requires random-access iterators for both the
pattern and the corpus.
</li>
</ul></div>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMoore.h7"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMoore.customization_points"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMoore.customization_points">Customization
points</a>
</h5>
<p>
The Boyer-Moore object takes a traits template parameter which enables the
caller to customize how one of the precomputed tables is stored. This table,
called the skip table, contains (logically) one entry for every possible
value that the pattern can contain. When searching 8-bit character data,
this table contains 256 elements. The traits class defines the table to be
used.
</p>
<p>
The default traits class uses a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code>
for small 'alphabets' and a <code class="computeroutput"><span class="identifier">tr1</span><span class="special">::</span><span class="identifier">unordered_map</span></code>
for larger ones. The array-based skip table gives excellent performance,
but could be prohibitively large when the 'alphabet' of elements to be searched
grows. The unordered_map based version only grows as the number of unique
elements in the pattern, but makes many more heap allocations, and gives
slower lookup performance.
</p>
<p>
To use a different skip table, you should define your own skip table object
and your own traits class, and use them to instantiate the Boyer-Moore object.
The interface to these objects is described TBD.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool"></a><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool" title="Boyer-Moore-Horspool Search">Boyer-Moore-Horspool
Search</a>
</h3></div></div></div>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h0"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.overview"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.overview">Overview</a>
</h5>
<p>
The header file 'boyer_moore_horspool.hpp' contains an implementation of
the Boyer-Moore-Horspool algorithm for searching sequences of values.
</p>
<p>
The Boyer-Moore-Horspool search algorithm was published by Nigel Horspool
in 1980. It is a refinement of the Boyer-Moore algorithm that trades space
for time. It uses less space for internal tables than Boyer-Moore, and has
poorer worst-case performance.
</p>
<p>
The Boyer-Moore-Horspool algorithm cannot be used with comparison predicates
like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">search</span></code>.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h1"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.interface"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.interface">Interface</a>
</h5>
<p>
Nomenclature: I refer to the sequence being searched for as the "pattern",
and the sequence being searched in as the "corpus".
</p>
<p>
For flexibility, the Boyer-Moore-Horspool algorithm has two interfaces; an
object-based interface and a procedural one. The object-based interface builds
the tables in the constructor, and uses operator () to perform the search.
The procedural interface builds the table and does the search all in one
step. If you are going to be searching for the same pattern in multiple corpora,
then you should use the object interface, and only build the tables once.
</p>
<p>
Here is the object interface:
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">patIter</span><span class="special">></span>
<span class="keyword">class</span> <span class="identifier">boyer_moore_horspool</span> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">boyer_moore_horspool</span> <span class="special">(</span> <span class="identifier">patIter</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">patIter</span> <span class="identifier">last</span> <span class="special">);</span>
<span class="special">~</span><span class="identifier">boyer_moore_horspool</span> <span class="special">();</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">corpusIter</span><span class="special">></span>
<span class="identifier">corpusIter</span> <span class="keyword">operator</span> <span class="special">()</span> <span class="special">(</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_first</span><span class="special">,</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_last</span> <span class="special">);</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
and here is the corresponding procedural interface:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">patIter</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">corpusIter</span><span class="special">></span>
<span class="identifier">corpusIter</span> <span class="identifier">boyer_moore_horspool_search</span> <span class="special">(</span>
<span class="identifier">corpusIter</span> <span class="identifier">corpus_first</span><span class="special">,</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_last</span><span class="special">,</span>
<span class="identifier">patIter</span> <span class="identifier">pat_first</span><span class="special">,</span> <span class="identifier">patIter</span> <span class="identifier">pat_last</span> <span class="special">);</span>
</pre>
<p>
</p>
<p>
Each of the functions is passed two pairs of iterators. The first two define
the corpus and the second two define the pattern. Note that the two pairs
need not be of the same type, but they do need to "point" at the
same type. In other words, <code class="computeroutput"><span class="identifier">patIter</span><span class="special">::</span><span class="identifier">value_type</span></code>
and <code class="computeroutput"><span class="identifier">curpusIter</span><span class="special">::</span><span class="identifier">value_type</span></code> need to be the same type.
</p>
<p>
The return value of the function is an iterator pointing to the start of
the pattern in the corpus. If the pattern is not found, it returns the end
of the corpus (<code class="computeroutput"><span class="identifier">corpus_last</span></code>).
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h2"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.performance"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.performance">Performance</a>
</h5>
<p>
The execution time of the Boyer-Moore-Horspool algorithm is linear in the
size of the string being searched; it can have a significantly lower constant
factor than many other search algorithms: it doesn't need to check every
character of the string to be searched, but rather skips over some of them.
Generally the algorithm gets faster as the pattern being searched for becomes
longer. Its efficiency derives from the fact that with each unsuccessful
attempt to find a match between the search string and the text it is searching,
it uses the information gained from that attempt to rule out as many positions
of the text as possible where the string cannot match.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h3"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.memory_use"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.memory_use">Memory
Use</a>
</h5>
<p>
The algorithm an internal table that has one entry for each member of the
"alphabet" in the pattern. For (8-bit) character types, this table
contains 256 entries.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h4"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.complexity"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.complexity">Complexity</a>
</h5>
<p>
The worst-case performance is <span class="emphasis"><em>O(m x n)</em></span>, where <span class="emphasis"><em>m</em></span>
is the length of the pattern and <span class="emphasis"><em>n</em></span> is the length of
the corpus. The average time is <span class="emphasis"><em>O(n)</em></span>. The best case
performance is sub-linear, and is, in fact, identical to Boyer-Moore, but
the initialization is quicker and the internal loop is simpler than Boyer-Moore.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h5"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.exception_safety"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.exception_safety">Exception
Safety</a>
</h5>
<p>
Both the object-oriented and procedural versions of the Boyer-Moore-Horspool
algorithm take their parameters by value and do not use any information other
than what is passed in. Therefore, both interfaces provide the strong exception
guarantee.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h6"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.notes"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.notes">Notes</a>
</h5>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
When using the object-based interface, the pattern must remain unchanged
for during the searches; i.e, from the time the object is constructed
until the final call to operator () returns.
</li>
<li class="listitem">
The Boyer-Moore-Horspool algorithm requires random-access iterators for
both the pattern and the corpus.
</li>
</ul></div>
<h5>
<a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.h7"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.BoyerMooreHorspool.customization_points"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.BoyerMooreHorspool.customization_points">Customization
points</a>
</h5>
<p>
The Boyer-Moore-Horspool object takes a traits template parameter which enables
the caller to customize how the precomputed table is stored. This table,
called the skip table, contains (logically) one entry for every possible
value that the pattern can contain. When searching 8-bit character data,
this table contains 256 elements. The traits class defines the table to be
used.
</p>
<p>
The default traits class uses a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code>
for small 'alphabets' and a <code class="computeroutput"><span class="identifier">tr1</span><span class="special">::</span><span class="identifier">unordered_map</span></code>
for larger ones. The array-based skip table gives excellent performance,
but could be prohibitively large when the 'alphabet' of elements to be searched
grows. The unordered_map based version only grows as the number of unique
elements in the pattern, but makes many more heap allocations, and gives
slower lookup performance.
</p>
<p>
To use a different skip table, you should define your own skip table object
and your own traits class, and use them to instantiate the Boyer-Moore-Horspool
object. The interface to these objects is described TBD.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt"></a><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt" title="Knuth-Morris-Pratt Search">Knuth-Morris-Pratt
Search</a>
</h3></div></div></div>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h0"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.overview"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.overview">Overview</a>
</h5>
<p>
The header file 'knuth_morris_pratt.hpp' contains an implementation of the
Knuth-Morris-Pratt algorithm for searching sequences of values.
</p>
<p>
The basic premise of the Knuth-Morris-Pratt algorithm is that when a mismatch
occurs, there is information in the pattern being searched for that can be
used to determine where the next match could begin, enabling the skipping
of some elements of the corpus that have already been examined.
</p>
<p>
It does this by building a table from the pattern being searched for, with
one entry for each element in the pattern.
</p>
<p>
The algorithm was conceived in 1974 by Donald Knuth and Vaughan Pratt, and
independently by James H. Morris. The three published it jointly in 1977
in the SIAM Journal on Computing <a href="http://citeseer.ist.psu.edu/context/23820/0" target="_top">http://citeseer.ist.psu.edu/context/23820/0</a>
</p>
<p>
However, the Knuth-Morris-Pratt algorithm cannot be used with comparison
predicates like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">search</span></code>.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h1"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.interface"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.interface">Interface</a>
</h5>
<p>
Nomenclature: I refer to the sequence being searched for as the "pattern",
and the sequence being searched in as the "corpus".
</p>
<p>
For flexibility, the Knuth-Morris-Pratt algorithm has two interfaces; an
object-based interface and a procedural one. The object-based interface builds
the table in the constructor, and uses operator () to perform the search.
The procedural interface builds the table and does the search all in one
step. If you are going to be searching for the same pattern in multiple corpora,
then you should use the object interface, and only build the tables once.
</p>
<p>
Here is the object interface:
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">patIter</span><span class="special">></span>
<span class="keyword">class</span> <span class="identifier">knuth_morris_pratt</span> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">knuth_morris_pratt</span> <span class="special">(</span> <span class="identifier">patIter</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">patIter</span> <span class="identifier">last</span> <span class="special">);</span>
<span class="special">~</span><span class="identifier">knuth_morris_pratt</span> <span class="special">();</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">corpusIter</span><span class="special">></span>
<span class="identifier">corpusIter</span> <span class="keyword">operator</span> <span class="special">()</span> <span class="special">(</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_first</span><span class="special">,</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_last</span> <span class="special">);</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
and here is the corresponding procedural interface:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">patIter</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">corpusIter</span><span class="special">></span>
<span class="identifier">corpusIter</span> <span class="identifier">knuth_morris_pratt_search</span> <span class="special">(</span>
<span class="identifier">corpusIter</span> <span class="identifier">corpus_first</span><span class="special">,</span> <span class="identifier">corpusIter</span> <span class="identifier">corpus_last</span><span class="special">,</span>
<span class="identifier">patIter</span> <span class="identifier">pat_first</span><span class="special">,</span> <span class="identifier">patIter</span> <span class="identifier">pat_last</span> <span class="special">);</span>
</pre>
<p>
</p>
<p>
Each of the functions is passed two pairs of iterators. The first two define
the corpus and the second two define the pattern. Note that the two pairs
need not be of the same type, but they do need to "point" at the
same type. In other words, <code class="computeroutput"><span class="identifier">patIter</span><span class="special">::</span><span class="identifier">value_type</span></code>
and <code class="computeroutput"><span class="identifier">curpusIter</span><span class="special">::</span><span class="identifier">value_type</span></code> need to be the same type.
</p>
<p>
The return value of the function is an iterator pointing to the start of
the pattern in the corpus. If the pattern is not found, it returns the end
of the corpus (<code class="computeroutput"><span class="identifier">corpus_last</span></code>).
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h2"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.performance"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.performance">Performance</a>
</h5>
<p>
The execution time of the Knuth-Morris-Pratt algorithm is linear in the size
of the string being searched. Generally the algorithm gets faster as the
pattern being searched for becomes longer. Its efficiency derives from the
fact that with each unsuccessful attempt to find a match between the search
string and the text it is searching, it uses the information gained from
that attempt to rule out as many positions of the text as possible where
the string cannot match.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h3"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.memory_use"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.memory_use">Memory
Use</a>
</h5>
<p>
The algorithm an that contains one entry for each element the pattern, plus
one extra. So, when searching for a 1026 byte string, the table will have
1027 entries.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h4"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.complexity"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.complexity">Complexity</a>
</h5>
<p>
The worst-case performance is <span class="emphasis"><em>O(2n)</em></span>, where <span class="emphasis"><em>n</em></span>
is the length of the corpus. The average time is <span class="emphasis"><em>O(n)</em></span>.
The best case performance is sub-linear.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h5"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.exception_safety"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.exception_safety">Exception
Safety</a>
</h5>
<p>
Both the object-oriented and procedural versions of the Knuth-Morris-Pratt
algorithm take their parameters by value and do not use any information other
than what is passed in. Therefore, both interfaces provide the strong exception
guarantee.
</p>
<h5>
<a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.h6"></a>
<span class="phrase"><a name="the_boost_algorithm_library.Searching.KnuthMorrisPratt.notes"></a></span><a class="link" href="Searching.html#the_boost_algorithm_library.Searching.KnuthMorrisPratt.notes">Notes</a>
</h5>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
When using the object-based interface, the pattern must remain unchanged
for during the searches; i.e, from the time the object is constructed
until the final call to operator () returns.
</li>
<li class="listitem">
The Knuth-Morris-Pratt algorithm requires random-access iterators for
both the pattern and the corpus. It should be possible to write this
to use bidirectional iterators (or possibly even forward ones), but this
implementation does not do that.
</li>
</ul></div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2010-2012 Marshall Clow<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div></td>
</tr></table>
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