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72 lines
2.6 KiB
ReStructuredText
72 lines
2.6 KiB
ReStructuredText
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.. Copyright David Abrahams 2006. Distributed under the Boost
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.. Software License, Version 1.0. (See accompanying
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.. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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::
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using namespace boost;
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int i = 0;
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typedef std::vector< int > element_range_type;
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typedef std::list< int > index_type;
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static const int element_range_size = 10;
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static const int index_size = 4;
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element_range_type elements( element_range_size );
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for(element_range_type::iterator el_it = elements.begin() ; el_it != elements.end() ; ++el_it)
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*el_it = std::distance(elements.begin(), el_it);
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index_type indices( index_size );
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for(index_type::iterator i_it = indices.begin() ; i_it != indices.end() ; ++i_it )
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*i_it = element_range_size - index_size + std::distance(indices.begin(), i_it);
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std::reverse( indices.begin(), indices.end() );
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typedef permutation_iterator< element_range_type::iterator, index_type::iterator > permutation_type;
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permutation_type begin = make_permutation_iterator( elements.begin(), indices.begin() );
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permutation_type it = begin;
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permutation_type end = make_permutation_iterator( elements.begin(), indices.end() );
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std::cout << "The original range is : ";
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std::copy( elements.begin(), elements.end(), std::ostream_iterator< int >( std::cout, " " ) );
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std::cout << "\n";
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std::cout << "The reindexing scheme is : ";
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std::copy( indices.begin(), indices.end(), std::ostream_iterator< int >( std::cout, " " ) );
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std::cout << "\n";
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std::cout << "The permutated range is : ";
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std::copy( begin, end, std::ostream_iterator< int >( std::cout, " " ) );
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std::cout << "\n";
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std::cout << "Elements at even indices in the permutation : ";
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it = begin;
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for(i = 0; i < index_size / 2 ; ++i, it+=2 ) std::cout << *it << " ";
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std::cout << "\n";
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std::cout << "Permutation backwards : ";
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it = begin + (index_size);
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assert( it != begin );
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for( ; it-- != begin ; ) std::cout << *it << " ";
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std::cout << "\n";
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std::cout << "Iterate backward with stride 2 : ";
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it = begin + (index_size - 1);
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for(i = 0 ; i < index_size / 2 ; ++i, it-=2 ) std::cout << *it << " ";
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std::cout << "\n";
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The output is::
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The original range is : 0 1 2 3 4 5 6 7 8 9
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The reindexing scheme is : 9 8 7 6
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The permutated range is : 9 8 7 6
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Elements at even indices in the permutation : 9 7
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Permutation backwards : 6 7 8 9
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Iterate backward with stride 2 : 6 8
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The source code for this example can be found `here`__.
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__ ../example/permutation_iter_example.cpp
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