boost/algorithm/searching/knuth_morris_pratt.hpp
/*
Copyright (c) Marshall Clow 2010-2012.
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
For more information, see http://www.boost.org
*/
#ifndef BOOST_ALGORITHM_KNUTH_MORRIS_PRATT_SEARCH_HPP
#define BOOST_ALGORITHM_KNUTH_MORRIS_PRATT_SEARCH_HPP
#include <vector>
#include <iterator> // for std::iterator_traits
#include <boost/config.hpp>
#include <boost/assert.hpp>
#include <boost/static_assert.hpp>
#include <boost/range/begin.hpp>
#include <boost/range/end.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/algorithm/searching/detail/debugging.hpp>
// #define BOOST_ALGORITHM_KNUTH_MORRIS_PRATT_DEBUG
namespace boost { namespace algorithm {
// #define NEW_KMP
/*
A templated version of the Knuth-Morris-Pratt searching algorithm.
Requirements:
* Random-access iterators
* The two iterator types (I1 and I2) must "point to" the same underlying type.
http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
http://www.inf.fh-flensburg.de/lang/algorithmen/pattern/kmpen.htm
*/
template <typename patIter>
class knuth_morris_pratt {
typedef typename std::iterator_traits<patIter>::difference_type difference_type;
public:
knuth_morris_pratt ( patIter first, patIter last )
: pat_first ( first ), pat_last ( last ),
k_pattern_length ( std::distance ( pat_first, pat_last )),
skip_ ( k_pattern_length + 1 ) {
#ifdef NEW_KMP
preKmp ( pat_first, pat_last );
#else
init_skip_table ( pat_first, pat_last );
#endif
#ifdef BOOST_ALGORITHM_KNUTH_MORRIS_PRATT_DEBUG
detail::PrintTable ( skip_.begin (), skip_.end ());
#endif
}
~knuth_morris_pratt () {}
/// \fn operator ( corpusIter corpus_first, corpusIter corpus_last, Pred p )
/// \brief Searches the corpus for the pattern that was passed into the constructor
///
/// \param corpus_first The start of the data to search (Random Access Iterator)
/// \param corpus_last One past the end of the data to search
/// \param p A predicate used for the search comparisons.
///
template <typename corpusIter>
std::pair<corpusIter, corpusIter>
operator () ( corpusIter corpus_first, corpusIter corpus_last ) const {
BOOST_STATIC_ASSERT (( boost::is_same<
typename std::iterator_traits<patIter>::value_type,
typename std::iterator_traits<corpusIter>::value_type>::value ));
if ( corpus_first == corpus_last ) return std::make_pair(corpus_last, corpus_last); // if nothing to search, we didn't find it!
if ( pat_first == pat_last ) return std::make_pair(corpus_first, corpus_first); // empty pattern matches at start
const difference_type k_corpus_length = std::distance ( corpus_first, corpus_last );
// If the pattern is larger than the corpus, we can't find it!
if ( k_corpus_length < k_pattern_length )
return std::make_pair(corpus_last, corpus_last);
return do_search ( corpus_first, corpus_last, k_corpus_length );
}
template <typename Range>
std::pair<typename boost::range_iterator<Range>::type, typename boost::range_iterator<Range>::type>
operator () ( Range &r ) const {
return (*this) (boost::begin(r), boost::end(r));
}
private:
/// \cond DOXYGEN_HIDE
patIter pat_first, pat_last;
const difference_type k_pattern_length;
std::vector <difference_type> skip_;
/// \fn operator ( corpusIter corpus_first, corpusIter corpus_last, Pred p )
/// \brief Searches the corpus for the pattern that was passed into the constructor
///
/// \param corpus_first The start of the data to search (Random Access Iterator)
/// \param corpus_last One past the end of the data to search
/// \param p A predicate used for the search comparisons.
///
template <typename corpusIter>
std::pair<corpusIter, corpusIter>
do_search ( corpusIter corpus_first, corpusIter corpus_last,
difference_type k_corpus_length ) const {
difference_type match_start = 0; // position in the corpus that we're matching
#ifdef NEW_KMP
int patternIdx = 0;
while ( match_start < k_corpus_length ) {
while ( patternIdx > -1 && pat_first[patternIdx] != corpus_first [match_start] )
patternIdx = skip_ [patternIdx]; //<--- Shifting the pattern on mismatch
patternIdx++;
match_start++; //<--- corpus is always increased by 1
if ( patternIdx >= (int) k_pattern_length )
return corpus_first + match_start - patternIdx;
}
#else
// At this point, we know:
// k_pattern_length <= k_corpus_length
// for all elements of skip, it holds -1 .. k_pattern_length
//
// In the loop, we have the following invariants
// idx is in the range 0 .. k_pattern_length
// match_start is in the range 0 .. k_corpus_length - k_pattern_length + 1
const difference_type last_match = k_corpus_length - k_pattern_length;
difference_type idx = 0; // position in the pattern we're comparing
while ( match_start <= last_match ) {
while ( pat_first [ idx ] == corpus_first [ match_start + idx ] ) {
if ( ++idx == k_pattern_length )
return std::make_pair(corpus_first + match_start, corpus_first + match_start + k_pattern_length);
}
// Figure out where to start searching again
// assert ( idx - skip_ [ idx ] > 0 ); // we're always moving forward
match_start += idx - skip_ [ idx ];
idx = skip_ [ idx ] >= 0 ? skip_ [ idx ] : 0;
// assert ( idx >= 0 && idx < k_pattern_length );
}
#endif
// We didn't find anything
return std::make_pair(corpus_last, corpus_last);
}
void preKmp ( patIter first, patIter last ) {
const difference_type count = std::distance ( first, last );
difference_type i, j;
i = 0;
j = skip_[0] = -1;
while (i < count) {
while (j > -1 && first[i] != first[j])
j = skip_[j];
i++;
j++;
if (first[i] == first[j])
skip_[i] = skip_[j];
else
skip_[i] = j;
}
}
void init_skip_table ( patIter first, patIter last ) {
const difference_type count = std::distance ( first, last );
difference_type j;
skip_ [ 0 ] = -1;
for ( int i = 1; i <= count; ++i ) {
j = skip_ [ i - 1 ];
while ( j >= 0 ) {
if ( first [ j ] == first [ i - 1 ] )
break;
j = skip_ [ j ];
}
skip_ [ i ] = j + 1;
}
}
// \endcond
};
/* Two ranges as inputs gives us four possibilities; with 2,3,3,4 parameters
Use a bit of TMP to disambiguate the 3-argument templates */
/// \fn knuth_morris_pratt_search ( corpusIter corpus_first, corpusIter corpus_last,
/// patIter pat_first, patIter pat_last )
/// \brief Searches the corpus for the pattern.
///
/// \param corpus_first The start of the data to search (Random Access Iterator)
/// \param corpus_last One past the end of the data to search
/// \param pat_first The start of the pattern to search for (Random Access Iterator)
/// \param pat_last One past the end of the data to search for
///
template <typename patIter, typename corpusIter>
std::pair<corpusIter, corpusIter> knuth_morris_pratt_search (
corpusIter corpus_first, corpusIter corpus_last,
patIter pat_first, patIter pat_last )
{
knuth_morris_pratt<patIter> kmp ( pat_first, pat_last );
return kmp ( corpus_first, corpus_last );
}
template <typename PatternRange, typename corpusIter>
std::pair<corpusIter, corpusIter> knuth_morris_pratt_search (
corpusIter corpus_first, corpusIter corpus_last, const PatternRange &pattern )
{
typedef typename boost::range_iterator<const PatternRange>::type pattern_iterator;
knuth_morris_pratt<pattern_iterator> kmp ( boost::begin(pattern), boost::end (pattern));
return kmp ( corpus_first, corpus_last );
}
template <typename patIter, typename CorpusRange>
typename boost::disable_if_c<
boost::is_same<CorpusRange, patIter>::value,
std::pair<typename boost::range_iterator<CorpusRange>::type, typename boost::range_iterator<CorpusRange>::type> >
::type
knuth_morris_pratt_search ( CorpusRange &corpus, patIter pat_first, patIter pat_last )
{
knuth_morris_pratt<patIter> kmp ( pat_first, pat_last );
return kmp (boost::begin (corpus), boost::end (corpus));
}
template <typename PatternRange, typename CorpusRange>
std::pair<typename boost::range_iterator<CorpusRange>::type, typename boost::range_iterator<CorpusRange>::type>
knuth_morris_pratt_search ( CorpusRange &corpus, const PatternRange &pattern )
{
typedef typename boost::range_iterator<const PatternRange>::type pattern_iterator;
knuth_morris_pratt<pattern_iterator> kmp ( boost::begin(pattern), boost::end (pattern));
return kmp (boost::begin (corpus), boost::end (corpus));
}
// Creator functions -- take a pattern range, return an object
template <typename Range>
boost::algorithm::knuth_morris_pratt<typename boost::range_iterator<const Range>::type>
make_knuth_morris_pratt ( const Range &r ) {
return boost::algorithm::knuth_morris_pratt
<typename boost::range_iterator<const Range>::type> (boost::begin(r), boost::end(r));
}
template <typename Range>
boost::algorithm::knuth_morris_pratt<typename boost::range_iterator<Range>::type>
make_knuth_morris_pratt ( Range &r ) {
return boost::algorithm::knuth_morris_pratt
<typename boost::range_iterator<Range>::type> (boost::begin(r), boost::end(r));
}
}}
#endif // BOOST_ALGORITHM_KNUTH_MORRIS_PRATT_SEARCH_HPP