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Diffstat (limited to 'src/boost/libs/multi_index/example/rearrange.cpp')
-rw-r--r-- | src/boost/libs/multi_index/example/rearrange.cpp | 265 |
1 files changed, 265 insertions, 0 deletions
diff --git a/src/boost/libs/multi_index/example/rearrange.cpp b/src/boost/libs/multi_index/example/rearrange.cpp new file mode 100644 index 000000000..31388513d --- /dev/null +++ b/src/boost/libs/multi_index/example/rearrange.cpp @@ -0,0 +1,265 @@ +/* Boost.MultiIndex example of use of rearrange facilities. + * + * Copyright 2003-2015 Joaquin M Lopez Munoz. + * 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) + * + * See http://www.boost.org/libs/multi_index for library home page. + */ + +#if !defined(NDEBUG) +#define BOOST_MULTI_INDEX_ENABLE_INVARIANT_CHECKING +#define BOOST_MULTI_INDEX_ENABLE_SAFE_MODE +#endif + +#include <boost/config.hpp> +#include <boost/detail/iterator.hpp> +#include <boost/multi_index_container.hpp> +#include <boost/multi_index/random_access_index.hpp> +#include <boost/random/binomial_distribution.hpp> +#include <boost/random/uniform_real.hpp> +#include <boost/random/mersenne_twister.hpp> +#include <algorithm> +#include <iostream> +#include <iterator> +#include <vector> + +#if !defined(BOOST_NO_CXX11_HDR_RANDOM) +#include <random> +#endif + +using boost::multi_index_container; +using namespace boost::multi_index; + +/* We model a card deck with a random access array containing + * card numbers (from 0 to 51), supplemented with an additional + * index which retains the start ordering. + */ + +class deck +{ + BOOST_STATIC_CONSTANT(std::size_t,num_cards=52); + + typedef multi_index_container< + int, + indexed_by< + random_access<>, /* base index */ + random_access<> /* "start" index */ + > + > container_type; + container_type cont; + +public: + deck() + { + cont.reserve(num_cards); + get<1>(cont).reserve(num_cards); + for(std::size_t i=0;i<num_cards;++i)cont.push_back(i); + } + + typedef container_type::iterator iterator; + typedef container_type::size_type size_type; + + iterator begin()const{return cont.begin();} + iterator end()const{return cont.end();} + size_type size()const{return cont.size();} + + template<typename InputIterator> + void rearrange(InputIterator it) + { + cont.rearrange(it); + } + + void reset() + { + /* simply rearrange the base index like the start index */ + + cont.rearrange(get<1>(cont).begin()); + } + + std::size_t position(int i)const + { + /* The position of a card in the deck is calculated by locating + * the card through the start index (which is ordered), projecting + * to the base index and diffing with the begin position. + * Resulting complexity: constant. + */ + + return project<0>(cont,get<1>(cont).begin()+i)-cont.begin(); + } + + std::size_t rising_sequences()const + { + /* Iterate through all cards and increment the sequence count + * when the current position is left to the previous. + * Resulting complexity: O(n), n=num_cards. + */ + + std::size_t s=1; + std::size_t last_pos=0; + + for(std::size_t i=0;i<num_cards;++i){ + std::size_t pos=position(i); + if(pos<last_pos)++s; + last_pos=pos; + } + + return s; + } +}; + +/* A vector of reference_wrappers to deck elements can be used + * as a view to the deck container. + * We use a special implicit_reference_wrapper having implicit + * ctor from its base type, as this simplifies the use of generic + * techniques on the resulting data structures. + */ + +template<typename T> +class implicit_reference_wrapper:public boost::reference_wrapper<T> +{ +private: + typedef boost::reference_wrapper<T> super; +public: + implicit_reference_wrapper(T& t):super(t){} +}; + +typedef std::vector<implicit_reference_wrapper<const int> > deck_view; + +/* Riffle shuffle is modeled like this: A cut is selected in the deck + * following a binomial distribution. Then, cards are randomly selected + * from one packet or the other with probability proportional to + * packet size. + */ + +template<typename RandomAccessIterator,typename OutputIterator> +void riffle_shuffle( + RandomAccessIterator first,RandomAccessIterator last, + OutputIterator out) +{ + static boost::mt19937 rnd_gen; + + typedef typename boost::detail::iterator_traits< + RandomAccessIterator>::difference_type difference_type; + typedef boost::binomial_distribution< + difference_type> rnd_cut_select_type; + typedef boost::uniform_real<> rnd_deck_select_type; + + rnd_cut_select_type cut_select(last-first); + RandomAccessIterator middle=first+cut_select(rnd_gen); + difference_type s0=middle-first; + difference_type s1=last-middle; + rnd_deck_select_type deck_select; + + while(s0!=0&&s1!=0){ + if(deck_select(rnd_gen)<(double)s0/(s0+s1)){ + *out++=*first++; + --s0; + } + else{ + *out++=*middle++; + --s1; + } + } + std::copy(first,first+s0,out); + std::copy(middle,middle+s1,out); +} + +struct riffle_shuffler +{ + void operator()(deck& d)const + { + dv.clear(); + dv.reserve(d.size()); + riffle_shuffle( + d.begin(),d.end(),std::back_inserter(dv)); /* do the shuffling */ + d.rearrange(dv.begin()); /* apply to the deck */ + } + +private: + mutable deck_view dv; +}; + +/* A truly random shuffle (up to stdlib implementation quality) using + * std::shuffle. + */ + +struct random_shuffler +{ + void operator()(deck& d) + { + dv.clear(); + dv.reserve(d.size()); + std::copy(d.begin(),d.end(),std::back_inserter(dv)); + shuffle_view(); + d.rearrange(dv.begin()); /* apply to the deck */ + } + +private: + deck_view dv; + +#if !defined(BOOST_NO_CXX11_HDR_RANDOM) + std::mt19937 e; + + void shuffle_view() + { + std::shuffle(dv.begin(),dv.end(),e); + } +#else + /* for pre-C++11 compilers we use std::random_shuffle */ + + void shuffle_view() + { + std::random_shuffle(dv.begin(),dv.end()); + } +#endif +}; + +/* Repeat a given shuffling algorithm repeats_num times + * and obtain the resulting rising sequences number. Average + * for tests_num trials. + */ + +template<typename Shuffler> +double shuffle_test( + unsigned int repeats_num,unsigned int tests_num + BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(Shuffler)) +{ + deck d; + Shuffler sh; + unsigned long total=0; + + for(unsigned int n=0;n<tests_num;++n){ + for(unsigned m=0;m<repeats_num;++m)sh(d); + total+=d.rising_sequences(); + d.reset(); + } + + return (double)total/tests_num; +} + +int main() +{ + unsigned rifs_num=0; + unsigned tests_num=0; + + std::cout<<"number of riffle shuffles (vg 5):"; + std::cin>>rifs_num; + std::cout<<"number of tests (vg 1000):"; + std::cin>>tests_num; + + std::cout<<"shuffling..."<<std::endl; + + std::cout<<"riffle shuffling\n" + " avg number of rising sequences: " + <<shuffle_test<riffle_shuffler>(rifs_num,tests_num) + <<std::endl; + + std::cout<<"random shuffling\n" + " avg number of rising sequences: " + <<shuffle_test<random_shuffler>(1,tests_num) + <<std::endl; + + return 0; +} |