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  1. #include <iostream>
  2. #include <utility>
  3. #include <vector>
  4. #include <array>
  5. #include <iterator>
  6.  
  7. namespace details {
  8.         template<unsigned...>struct indexes { using type=indexes; };
  9.         template<unsigned max, unsigned... is>struct make_indexes:make_indexes<max-1, max-1, is...>{};
  10.         template<unsigned... is>struct make_indexes<0,is...>:indexes<is...>{};
  11.         template<unsigned max>using make_indexes_t=typename make_indexes<max>::type;
  12.  
  13.         template<bool b, class T=void>
  14.         using enable_if_t=typename std::enable_if<b,T>::type;
  15.         struct list_tag {};
  16.         struct from_iterator_tag {};
  17.  
  18.         template<unsigned N, class Iterator>
  19.         struct iterator_array {
  20.         private:
  21.             std::array<Iterator,N> raw;
  22.             size_t index = 0;
  23.  
  24.             static Iterator to_elem(Iterator& it, Iterator end, bool advance=true) {
  25.                 if (it == end) return end;
  26.                 if (advance) return ++it;
  27.                 return it;
  28.             }
  29.             template< unsigned...Is>
  30.             iterator_array( indexes<Is...>, from_iterator_tag, Iterator& it, Iterator end ):
  31.                 raw( {to_elem(it, end, false), (void(Is), to_elem(it,end))...} )
  32.             {}
  33.         public:
  34.             Iterator begin() const { return raw[index]; }
  35.             Iterator end() const { return std::next(raw[(index+N-1)%N]); }
  36.             void push_back( Iterator it ) {
  37.                 raw[index] = it;
  38.                 index = (index+1)%N;
  39.             }
  40.             iterator_array( from_iterator_tag, Iterator& it, Iterator end ):iterator_array( make_indexes<N-1>{}, from_iterator_tag{}, it, end ) {}
  41.             iterator_array( iterator_array const& o )=default;
  42.             iterator_array() = default; // invalid!
  43.             iterator_array& operator=( iterator_array const& o )=delete;
  44.             typedef decltype(*std::declval<Iterator>()) reference_type;
  45.             reference_type operator[](std::size_t i)const{return *(raw[ (i+index)%N ]);}
  46.         };
  47.  
  48.         struct sentinal_tag {};
  49.  
  50.         template<class I>using value_type_t=typename std::iterator_traits<I>::value_type;
  51.  
  52.         template<class I, unsigned N>
  53.         class slide_iterator:public std::iterator<
  54.             std::forward_iterator_tag,
  55.             iterator_array<N,I>,
  56.             iterator_array<N,I>*,
  57.             iterator_array<N,I> const&
  58.         > {
  59.             I current;
  60.             mutable bool bread = false;
  61.             typedef iterator_array<N,I> value_type;
  62.             mutable value_type data;
  63.             void ensure_read() const {
  64.                 if (!bread) {
  65.                     data.push_back(current);
  66.                 }
  67.                 bread = true;
  68.             }
  69.         public:
  70.             slide_iterator& operator++() { ensure_read(); ++current; bread=false; return *this; }
  71.             slide_iterator operator++(int) { slide_iterator retval=*this; ++*this; return retval; }
  72.             value_type const& operator*() const { ensure_read(); return data; }
  73.             bool operator==(slide_iterator const& o){return current==o.current;}
  74.             bool operator!=(slide_iterator const& o){return current!=o.current;}
  75.             bool operator<(slide_iterator const& o){return current<o.current;}
  76.             bool operator>(slide_iterator const& o){return current>o.current;}
  77.             bool operator<=(slide_iterator const& o){return current<=o.current;}
  78.             bool operator>=(slide_iterator const& o){return current>=o.current;}
  79.             explicit slide_iterator( I start, I end ):current(start), bread(true), data(from_iterator_tag{}, current, end) {}
  80.             explicit slide_iterator( sentinal_tag, I end ):current(end) {}
  81.  
  82.         };
  83.     }
  84.  
  85.     template<class Iterator, unsigned N>
  86.     struct slide_range_t {
  87.         using iterator=details::slide_iterator<Iterator, N>;
  88.         iterator b;
  89.         iterator e;
  90.         slide_range_t( Iterator start, Iterator end ):
  91.             b( start, end ),
  92.             e( details::sentinal_tag{}, end )
  93.         {}
  94.         slide_range_t( slide_range_t const& o )=default;
  95.         slide_range_t() = delete;
  96.         iterator begin() const { return b; }
  97.         iterator end() const { return e; }
  98.     };
  99.  
  100.     template<unsigned N, class Iterator>
  101.     slide_range_t< Iterator, N > slide_range( Iterator b, Iterator e ) {
  102.         return {b,e};
  103.     }
  104.  
  105. int main() {
  106.     std::vector<int> foo(33);
  107.     for (int i = 0; i < foo.size(); ++i)
  108.         foo[i]=i;
  109.     for( auto&& r:slide_range<3>(foo.begin(), foo.end()) ) {
  110.     	for (int x:r) {
  111.             std::cout << x << ",";
  112.         }
  113.     std::cout << "\n";
  114.     }
  115. }
Success #stdin #stdout 0s 3476KB
comments (?)
stdin
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Standard input is empty
stdout
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0,1,2,
1,2,3,
2,3,4,
3,4,5,
4,5,6,
5,6,7,
6,7,8,
7,8,9,
8,9,10,
9,10,11,
10,11,12,
11,12,13,
12,13,14,
13,14,15,
14,15,16,
15,16,17,
16,17,18,
17,18,19,
18,19,20,
19,20,21,
20,21,22,
21,22,23,
22,23,24,
23,24,25,
24,25,26,
25,26,27,
26,27,28,
27,28,29,
28,29,30,
29,30,31,
30,31,32,
https://ideone.com/GnI7OQ
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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