1// <experimental/algorithm> -*- C++ -*-
2
3// Copyright (C) 2014-2015 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
41namespace std _GLIBCXX_VISIBILITY(default)
42{
43namespace experimental
44{
45inline namespace fundamentals_v1
46{
47_GLIBCXX_BEGIN_NAMESPACE_VERSION
48
49  template<typename _ForwardIterator, typename _Searcher>
50    inline _ForwardIterator
51    search(_ForwardIterator __first, _ForwardIterator __last,
52	   const _Searcher& __searcher)
53    { return __searcher(__first, __last); }
54
55#define __cpp_lib_experimental_sample 201402
56
57  /// Reservoir sampling algorithm.
58  template<typename _InputIterator, typename _RandomAccessIterator,
59           typename _Size, typename _UniformRandomNumberGenerator>
60    _RandomAccessIterator
61    __sample(_InputIterator __first, _InputIterator __last, input_iterator_tag,
62	     _RandomAccessIterator __out, random_access_iterator_tag,
63	     _Size __n, _UniformRandomNumberGenerator&& __g)
64    {
65      using __distrib_type = std::uniform_int_distribution<_Size>;
66      using __param_type = typename __distrib_type::param_type;
67      __distrib_type __d{};
68      _Size __sample_sz = 0;
69      while (__first != __last && __sample_sz != __n)
70	__out[__sample_sz++] = *__first++;
71      for (auto __pop_sz = __sample_sz; __first != __last;
72	  ++__first, ++__pop_sz)
73	{
74	  const auto __k = __d(__g, __param_type{0, __pop_sz});
75	  if (__k < __n)
76	    __out[__k] = *__first;
77	}
78      return __out + __sample_sz;
79    }
80
81  /// Selection sampling algorithm.
82  template<typename _ForwardIterator, typename _OutputIterator, typename _Cat,
83           typename _Size, typename _UniformRandomNumberGenerator>
84    _OutputIterator
85    __sample(_ForwardIterator __first, _ForwardIterator __last,
86	     forward_iterator_tag,
87	     _OutputIterator __out, _Cat,
88	     _Size __n, _UniformRandomNumberGenerator&& __g)
89    {
90      using __distrib_type = std::uniform_int_distribution<_Size>;
91      using __param_type = typename __distrib_type::param_type;
92      __distrib_type __d{};
93      _Size __unsampled_sz = std::distance(__first, __last);
94      for (__n = std::min(__n, __unsampled_sz); __n != 0; ++__first)
95	if (__d(__g, __param_type{0, --__unsampled_sz}) < __n)
96	  {
97	    *__out++ = *__first;
98	    --__n;
99	  }
100      return __out;
101    }
102
103  /// Take a random sample from a population.
104  template<typename _PopulationIterator, typename _SampleIterator,
105           typename _Distance, typename _UniformRandomNumberGenerator>
106    _SampleIterator
107    sample(_PopulationIterator __first, _PopulationIterator __last,
108	   _SampleIterator __out, _Distance __n,
109	   _UniformRandomNumberGenerator&& __g)
110    {
111      using __pop_cat = typename
112	std::iterator_traits<_PopulationIterator>::iterator_category;
113      using __samp_cat = typename
114	std::iterator_traits<_SampleIterator>::iterator_category;
115
116      static_assert(
117	  __or_<is_convertible<__pop_cat, forward_iterator_tag>,
118		is_convertible<__samp_cat, random_access_iterator_tag>>::value,
119	  "output range must use a RandomAccessIterator when input range"
120	  " does not meet the ForwardIterator requirements");
121
122      static_assert(is_integral<_Distance>::value,
123		    "sample size must be an integer type");
124
125      return std::experimental::__sample(
126	  __first, __last, __pop_cat{}, __out, __samp_cat{},
127	  __n, std::forward<_UniformRandomNumberGenerator>(__g));
128    }
129
130_GLIBCXX_END_NAMESPACE_VERSION
131} // namespace fundamentals_v1
132} // namespace experimental
133} // namespace std
134
135#endif // C++14
136
137#endif // _GLIBCXX_EXPERIMENTAL_ALGORITHM
138