libstdc++
experimental/algorithm
Go to the documentation of this file.
1 // <experimental/algorithm> -*- C++ -*-
2 
3 // Copyright (C) 2014-2016 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file experimental/algorithm
26  * This is a TS C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_EXPERIMENTAL_ALGORITHM
30 #define _GLIBCXX_EXPERIMENTAL_ALGORITHM 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus <= 201103L
35 # include <bits/c++14_warning.h>
36 #else
37 
38 #include <algorithm>
39 #include <random>
40 #include <experimental/bits/lfts_config.h>
41 
42 namespace std _GLIBCXX_VISIBILITY(default)
43 {
44 namespace experimental
45 {
46 inline namespace fundamentals_v1
47 {
48 _GLIBCXX_BEGIN_NAMESPACE_VERSION
49 
50  template<typename _ForwardIterator, typename _Searcher>
51  inline _ForwardIterator
52  search(_ForwardIterator __first, _ForwardIterator __last,
53  const _Searcher& __searcher)
54  { return __searcher(__first, __last); }
55 
56 #define __cpp_lib_experimental_sample 201402
57 
58  /// Reservoir sampling algorithm.
59  template<typename _InputIterator, typename _RandomAccessIterator,
60  typename _Size, typename _UniformRandomNumberGenerator>
61  _RandomAccessIterator
62  __sample(_InputIterator __first, _InputIterator __last, input_iterator_tag,
63  _RandomAccessIterator __out, random_access_iterator_tag,
64  _Size __n, _UniformRandomNumberGenerator&& __g)
65  {
66  using __distrib_type = std::uniform_int_distribution<_Size>;
67  using __param_type = typename __distrib_type::param_type;
68  __distrib_type __d{};
69  _Size __sample_sz = 0;
70  while (__first != __last && __sample_sz != __n)
71  __out[__sample_sz++] = *__first++;
72  for (auto __pop_sz = __sample_sz; __first != __last;
73  ++__first, ++__pop_sz)
74  {
75  const auto __k = __d(__g, __param_type{0, __pop_sz});
76  if (__k < __n)
77  __out[__k] = *__first;
78  }
79  return __out + __sample_sz;
80  }
81 
82  /// Selection sampling algorithm.
83  template<typename _ForwardIterator, typename _OutputIterator, typename _Cat,
84  typename _Size, typename _UniformRandomNumberGenerator>
85  _OutputIterator
86  __sample(_ForwardIterator __first, _ForwardIterator __last,
87  forward_iterator_tag,
88  _OutputIterator __out, _Cat,
89  _Size __n, _UniformRandomNumberGenerator&& __g)
90  {
91  using __distrib_type = std::uniform_int_distribution<_Size>;
92  using __param_type = typename __distrib_type::param_type;
93  __distrib_type __d{};
94  _Size __unsampled_sz = std::distance(__first, __last);
95  for (__n = std::min(__n, __unsampled_sz); __n != 0; ++__first)
96  if (__d(__g, __param_type{0, --__unsampled_sz}) < __n)
97  {
98  *__out++ = *__first;
99  --__n;
100  }
101  return __out;
102  }
103 
104  /// Take a random sample from a population.
105  template<typename _PopulationIterator, typename _SampleIterator,
106  typename _Distance, typename _UniformRandomNumberGenerator>
107  _SampleIterator
108  sample(_PopulationIterator __first, _PopulationIterator __last,
109  _SampleIterator __out, _Distance __n,
110  _UniformRandomNumberGenerator&& __g)
111  {
112  using __pop_cat = typename
113  std::iterator_traits<_PopulationIterator>::iterator_category;
114  using __samp_cat = typename
115  std::iterator_traits<_SampleIterator>::iterator_category;
116 
117  static_assert(
118  __or_<is_convertible<__pop_cat, forward_iterator_tag>,
119  is_convertible<__samp_cat, random_access_iterator_tag>>::value,
120  "output range must use a RandomAccessIterator when input range"
121  " does not meet the ForwardIterator requirements");
122 
123  static_assert(is_integral<_Distance>::value,
124  "sample size must be an integer type");
125 
126  return std::experimental::__sample(
127  __first, __last, __pop_cat{}, __out, __samp_cat{},
128  __n, std::forward<_UniformRandomNumberGenerator>(__g));
129  }
130 
131 _GLIBCXX_END_NAMESPACE_VERSION
132 } // namespace fundamentals_v1
133 } // namespace experimental
134 } // namespace std
135 
136 #endif // C++14
137 
138 #endif // _GLIBCXX_EXPERIMENTAL_ALGORITHM