1 | #ifndef theplu_yat_random_copy_k_of_n |
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2 | #define theplu_yat_random_copy_k_of_n |
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3 | |
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4 | // $Id: copy_k_of_n.h 3792 2019-04-12 07:15:09Z peter $ |
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5 | |
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6 | /* |
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7 | Copyright (C) 2015, 2019 Peter Johansson |
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8 | |
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9 | This file is part of the yat library, http://dev.thep.lu.se/yat |
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10 | |
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11 | The yat library is free software; you can redistribute it and/or |
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12 | modify it under the terms of the GNU General Public License as |
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13 | published by the Free Software Foundation; either version 3 of the |
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14 | License, or (at your option) any later version. |
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15 | |
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16 | The yat library is distributed in the hope that it will be useful, |
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17 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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18 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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19 | General Public License for more details. |
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20 | |
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21 | You should have received a copy of the GNU General Public License |
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22 | along with yat. If not, see <http://www.gnu.org/licenses/>. |
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23 | */ |
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24 | |
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25 | #include "random.h" |
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26 | |
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27 | #include <yat/utility/yat_assert.h> |
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28 | |
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29 | #include <boost/concept_check.hpp> |
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30 | #include <boost/iterator/iterator_concepts.hpp> |
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31 | #include <boost/iterator/iterator_traits.hpp> |
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32 | |
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33 | namespace theplu { |
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34 | namespace yat { |
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35 | namespace random { |
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36 | |
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37 | /** |
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38 | Copy k random element out of range [it, it+n) into output range |
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39 | [out, out+k). |
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40 | |
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41 | Each element in the input range is copied with equal probability: |
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42 | k/n. |
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43 | |
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44 | Type Requirements: |
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45 | - \c InputIterator is \readable_iterator |
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46 | - \c InputIterator is \single_pass_iterator |
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47 | - \c OutputIterator is \writable_iterator |
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48 | - \c OutputIterator is \incrementable_iterator |
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49 | |
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50 | *out = *it is a valid expression if it is referencable. |
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51 | |
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52 | \return iterator one-passed the last element copied |
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53 | |
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54 | \since New in yat 0.14 |
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55 | */ |
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56 | template<typename InputIterator, typename Size1, typename Size2, |
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57 | typename OutputIterator> |
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58 | OutputIterator copy_k_of_n(InputIterator it, Size1 k, Size2 n, |
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59 | OutputIterator out) |
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60 | { |
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61 | BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIterator<InputIterator>)); |
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62 | BOOST_CONCEPT_ASSERT((boost_concepts::SinglePassIterator<InputIterator>)); |
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63 | |
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64 | typedef typename boost::iterator_value<InputIterator>::type value_type; |
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65 | // check that *out = *it is valid |
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66 | BOOST_CONCEPT_ASSERT((boost_concepts::WritableIterator<OutputIterator, value_type>)); |
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67 | BOOST_CONCEPT_ASSERT((boost_concepts::IncrementableIterator<OutputIterator>)); |
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68 | |
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69 | YAT_ASSERT( k <= n); |
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70 | |
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71 | DiscreteUniform rnd; |
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72 | while (n) { |
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73 | if (rnd(n)<static_cast<unsigned long int>(k)) { |
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74 | --k; |
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75 | *out = *it; |
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76 | ++out; |
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77 | } |
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78 | --n; |
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79 | ++it; |
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80 | } |
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81 | return out; |
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82 | } |
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83 | |
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84 | |
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85 | }}} // of namespace random, yat, and theplu |
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86 | |
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87 | #endif |
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