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diff --git a/doc/html/algorithm/Searching.html b/doc/html/algorithm/Searching.html new file mode 100644 index 0000000000..a9e743a139 --- /dev/null +++ b/doc/html/algorithm/Searching.html @@ -0,0 +1,544 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Searching Algorithms</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../algorithm.html" title="Chapter 3. The Boost Algorithm Library"> +<link rel="prev" href="../algorithm.html" title="Chapter 3. The Boost Algorithm Library"> +<link rel="next" href="CXX11.html" title="C++11 Algorithms"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="../algorithm.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../algorithm.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="CXX11.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<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> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="../algorithm.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../algorithm.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="CXX11.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |