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  1. // Experimental sliding window class. (3.00)
  2.  
  3. #include <iostream>
  4.  
  5. template<typename T>
  6. struct window_wrapper {
  7.     T m_first, m_last;
  8.     T begin() const
  9.     { return m_first; }
  10.     T end() const
  11.     { return m_last; }
  12. };
  13.  
  14. // class sliding_window
  15. // Group a sequence into sequential n-element chunks.
  16. // sliding_window(string("ABCDEF"), 4) -> ABCD, BCDE, CDEF
  17.  
  18. template<typename Iter>
  19. struct sliding_window {
  20.     typedef window_wrapper<Iter> value_type;
  21.  
  22.     template<typename Iterable>
  23.     sliding_window(Iterable&&, size_t n);
  24.     sliding_window(Iter, Iter, size_t n);
  25.  
  26.     sliding_window begin() const
  27.     { return *this; }
  28.     sliding_window end() const
  29.     { return sliding_window(m_last, m_last, 0); }
  30.  
  31.     value_type operator*() const
  32.     { return {m_first, std::next(m_next)}; }
  33.  
  34.     sliding_window& operator++()
  35.     { ++m_first; ++m_next; return *this; }
  36.     sliding_window operator++(int)
  37.     { sliding_window temp(*this); ++*this; return temp; }
  38.  
  39.     bool operator==(const sliding_window& other) const
  40.     { return m_next == other.m_next; }
  41.     bool operator!=(const sliding_window& other) const
  42.     { return !(*this == other); }
  43.  
  44. private:
  45.     Iter m_first, m_next, m_last;
  46. };
  47.  
  48. #if __cplusplus >= 201703L
  49. template<typename Iterable>
  50. sliding_window(Iterable&& t, size_t) ->
  51.     sliding_window<decltype(std::begin(t))>;
  52. #endif // C++17
  53.  
  54. template<typename Iter>
  55. template<typename Iterable>
  56. sliding_window<Iter>::sliding_window(Iterable&& v, size_t n)
  57. : sliding_window(std::begin(v), std::end(v), n)
  58. {}
  59.  
  60. template<typename Iter>
  61. sliding_window<Iter>::sliding_window(Iter first, Iter last, size_t n)
  62. : m_first(first), m_next(n > 0 ? first : last), m_last(last)
  63. {
  64.     for (size_t i = 1; i < n && m_next != m_last; i++)
  65.         ++m_next;
  66. }
  67.  
  68. // Ease creation of sliding windows.
  69. // (the C++17 deduction guides make these obsolete)
  70. template<typename Iter>
  71. auto make_sliding_window(Iter first, Iter last, size_t n)
  72. {
  73.     return sliding_window<decltype(first)>(first, last, n);
  74. }
  75.  
  76. template<typename Iterable>
  77. auto make_sliding_window(Iterable&& v, size_t n)
  78. {
  79.     return make_sliding_window(std::begin(v), std::end(v), n);
  80. }
  81.  
  82. // Testing.
  83.  
  84. int main()
  85. {
  86.     auto print = [](auto&& iterable) {
  87.         for (auto item : iterable) std::cout << item;
  88.         std::cout << ' ';
  89.     };
  90.  
  91.     std::string s = "ABCDEFGH";
  92.     std::cout << s << std::endl;
  93.  
  94.     // Ensure all constness and value categories compile.
  95.     make_sliding_window(s, 1);
  96.     make_sliding_window(const_cast<const std::string&>(s), 1);
  97.     make_sliding_window(std::string(), 1);
  98.  
  99.     for (size_t i = 0; i <= s.size()+1; i++) {
  100.         auto sw = make_sliding_window(s, i);
  101.         std::cout << i << "> ";
  102.         for (auto window : sw)
  103.             print(window);
  104.         std::cout << std::endl;
  105.     }
  106.  
  107.     for (size_t i = 0; i <= s.size()+1; i++) {
  108.         auto sw = make_sliding_window(s.begin(), s.end(), i);
  109.         std::cout << i << "> ";
  110.         for (auto window : sw)
  111.             print(window);
  112.         std::cout << std::endl;
  113.     }
  114.  
  115.     // Modify non-const sequence through window.
  116.     for (auto window : make_sliding_window(s, 1))
  117.         for (auto& x : window)
  118.             x = '-';
  119.     std::cout << s << std::endl;
  120. }
Success #stdin #stdout 0s 5284KB
comments (?)
stdin
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Standard input is empty
stdout
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ABCDEFGH
0> 
1> A B C D E F G H 
2> AB BC CD DE EF FG GH 
3> ABC BCD CDE DEF EFG FGH 
4> ABCD BCDE CDEF DEFG EFGH 
5> ABCDE BCDEF CDEFG DEFGH 
6> ABCDEF BCDEFG CDEFGH 
7> ABCDEFG BCDEFGH 
8> ABCDEFGH 
9> 
0> 
1> A B C D E F G H 
2> AB BC CD DE EF FG GH 
3> ABC BCD CDE DEF EFG FGH 
4> ABCD BCDE CDEF DEFG EFGH 
5> ABCDE BCDEF CDEFG DEFGH 
6> ABCDEF BCDEFG CDEFGH 
7> ABCDEFG BCDEFGH 
8> ABCDEFGH 
9> 
--------
https://ideone.com/5vGzkT
language:
C++ (gcc 8.3)
created:
94 days ago
visibility:
public

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