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include/boost/algorithm/cxx11/is_permutation.hpp

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+/*
+   Copyright (c) Marshall Clow 2011-2012.
+
+   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)
+*/
+
+/// \file  is_permutation.hpp
+/// \brief Is a sequence a permutation of another sequence
+/// \author Marshall Clow
+
+#ifndef BOOST_ALGORITHM_IS_PERMUTATION11_HPP
+#define BOOST_ALGORITHM_IS_PERMUTATION11_HPP
+
+#include <algorithm>    // for std::find_if, count_if, mismatch
+#include <utility>      // for std::pair
+#include <functional>   // for std::equal_to
+#include <iterator>
+
+#include <boost/config.hpp>
+#include <boost/range/begin.hpp>
+#include <boost/range/end.hpp>
+#include <boost/core/enable_if.hpp>
+#include <boost/type_traits/is_same.hpp>
+
+namespace boost { namespace algorithm {
+
+/// \cond DOXYGEN_HIDE
+namespace detail {
+    template <typename Predicate, typename Iterator>
+    struct value_predicate {
+        value_predicate ( Predicate p, Iterator it ) : p_ ( p ), it_ ( it ) {}
+
+        template <typename T1>
+        bool operator () ( const T1 &t1 ) const { return p_ ( *it_, t1 ); }
+    private:
+        Predicate p_;
+        Iterator it_;
+        };
+        
+//  Preconditions:
+//  1. The sequences are the same length
+//  2. Any common elements on the front have been removed (not necessary for correctness, just for performance)
+    template< class ForwardIterator1, class ForwardIterator2, class BinaryPredicate >
+    bool is_permutation_inner ( ForwardIterator1 first1, ForwardIterator1 last1,
+                                ForwardIterator2 first2, ForwardIterator2 last2,
+                                BinaryPredicate p ) {
+        //  for each unique value in the sequence [first1,last1), count how many times
+        //  it occurs, and make sure it occurs the same number of times in [first2, last2)
+            for ( ForwardIterator1 iter = first1; iter != last1; ++iter ) {
+                value_predicate<BinaryPredicate, ForwardIterator1> pred ( p, iter );
+
+            /*  For each value we haven't seen yet... */
+                if ( std::find_if ( first1, iter, pred ) == iter ) {
+                    std::size_t dest_count = std::count_if ( first2, last2, pred );
+                    if ( dest_count == 0 || dest_count != (std::size_t) std::count_if ( iter, last1, pred ))
+                        return false;
+                    }
+                }
+
+        return true;
+        }                      
+
+    template< class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
+    bool is_permutation_tag ( ForwardIterator1 first1, ForwardIterator1 last1, 
+                          ForwardIterator2 first2, ForwardIterator2 last2, 
+                          BinaryPredicate p,
+                          std::forward_iterator_tag, std::forward_iterator_tag ) {
+
+    //  Skip the common prefix (if any)
+        while ( first1 != last1 && first2 != last2 && p ( *first1, *first2 )) {
+            ++first1;
+            ++first2;
+            }
+        if ( first1 != last1 && first2 != last2 )
+            return boost::algorithm::detail::is_permutation_inner ( first1, last1, first2, last2,
+                std::equal_to<typename std::iterator_traits<ForwardIterator1>::value_type> ());
+        return first1 == last1 && first2 == last2;
+        }
+
+    template <class RandomAccessIterator1, class RandomAccessIterator2, class BinaryPredicate>
+    bool is_permutation_tag ( RandomAccessIterator1 first1, RandomAccessIterator1 last1, 
+                          RandomAccessIterator2 first2, RandomAccessIterator2 last2, 
+                          BinaryPredicate p,
+                          std::random_access_iterator_tag, std::random_access_iterator_tag ) {
+    //  Cheap check
+        if ( std::distance ( first1, last1 ) != std::distance ( first2, last2 ))
+            return false;
+    //  Skip the common prefix (if any)
+        while ( first1 != last1 && first2 != last2 && p ( *first1, *first2 )) {
+            ++first1;
+            ++first2;
+            }
+
+        if ( first1 != last1 && first2 != last2 )
+            return is_permutation_inner (first1, last1, first2, last2, p);
+        return first1 == last1 && first2 == last2;
+        }
+
+}
+/// \endcond
+
+/// \fn is_permutation ( ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 first2, BinaryPredicate p )
+/// \brief Tests to see if the sequence [first,last) is a permutation of the sequence starting at first2
+///
+/// \param first1   The start of the input sequence
+/// \param last1    One past the end of the input sequence
+/// \param first2   The start of the second sequence
+/// \param p        The predicate to compare elements with
+///
+/// \note           This function is part of the C++2011 standard library.
+template< class ForwardIterator1, class ForwardIterator2, class BinaryPredicate >
+bool is_permutation ( ForwardIterator1 first1, ForwardIterator1 last1,
+                      ForwardIterator2 first2, BinaryPredicate p )
+{
+//  Skip the common prefix (if any)
+    std::pair<ForwardIterator1, ForwardIterator2> eq = std::mismatch (first1, last1, first2, p);
+    first1 = eq.first;
+    first2 = eq.second;
+    if ( first1 != last1 ) {
+    //  Create last2
+        ForwardIterator2 last2 = first2;
+        std::advance ( last2, std::distance (first1, last1));
+        return boost::algorithm::detail::is_permutation_inner ( first1, last1, first2, last2, p );
+        }
+
+    return true;
+}
+
+/// \fn is_permutation ( ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 first2 )
+/// \brief Tests to see if the sequence [first,last) is a permutation of the sequence starting at first2
+///
+/// \param first1   The start of the input sequence
+/// \param last2    One past the end of the input sequence
+/// \param first2   The start of the second sequence
+/// \note           This function is part of the C++2011 standard library.
+template< class ForwardIterator1, class ForwardIterator2 >
+bool is_permutation ( ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2 )
+{
+//  How should I deal with the idea that ForwardIterator1::value_type
+//  and ForwardIterator2::value_type could be different? Define my own comparison predicate?
+//  Skip the common prefix (if any)
+    std::pair<ForwardIterator1, ForwardIterator2> eq = std::mismatch (first1, last1, first2 );
+    first1 = eq.first;
+    first2 = eq.second;
+    if ( first1 != last1 ) {
+    //  Create last2
+        ForwardIterator2 last2 = first2;
+        std::advance ( last2, std::distance (first1, last1));
+        return boost::algorithm::detail::is_permutation_inner ( first1, last1, first2, last2,
+            std::equal_to<typename std::iterator_traits<ForwardIterator1>::value_type> ());
+        }
+    return true;
+}
+
+
+/// \fn is_permutation ( const Range &r, ForwardIterator first2 )
+/// \brief Tests to see if the sequence [first,last) is a permutation of the sequence starting at first2
+///
+/// \param r        The input range
+/// \param first2   The start of the second sequence
+template <typename Range, typename ForwardIterator>
+bool is_permutation ( const Range &r, ForwardIterator first2 )
+{
+    return boost::algorithm::is_permutation (boost::begin (r), boost::end (r), first2 );
+}
+
+/// \fn is_permutation ( const Range &r, ForwardIterator first2, BinaryPredicate pred )
+/// \brief Tests to see if the sequence [first,last) is a permutation of the sequence starting at first2
+///
+/// \param r        The input range
+/// \param first2   The start of the second sequence
+/// \param pred     The predicate to compare elements with
+///
+//  Disable this template when the first two parameters are the same type
+//  That way the non-range version will be chosen.
+template <typename Range, typename ForwardIterator, typename BinaryPredicate>
+typename boost::disable_if_c<boost::is_same<Range, ForwardIterator>::value, bool>::type
+is_permutation ( const Range &r, ForwardIterator first2, BinaryPredicate pred )
+{
+    return boost::algorithm::is_permutation (boost::begin (r), boost::end (r), first2, pred );
+}
+
+}}
+
+#endif  // BOOST_ALGORITHM_IS_PERMUTATION11_HPP