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/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