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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. template<class T, size_t MaxSize>
  5. class TopN
  6. {
  7. public:
  8.     void push_back(T v)
  9.     {
  10.         if (m_vector.size() < MaxSize)
  11.             m_vector.push_back(v);
  12.         else
  13.             m_vector[m_pos] = v;
  14.  
  15.         if (++m_pos == MaxSize)
  16.             m_pos = 0;
  17.     }
  18.  
  19.     class DummyIterator
  20.     {
  21.     public:
  22.         TopN &r; // a direct reference to our boss.
  23.         int p, m; // m: how many elements we can pull from vector, p: position of the cursor.
  24.  
  25.         DummyIterator(TopN& t) : r(t), p(t.m_pos), m(t.m_vector.size()){}
  26.  
  27.         operator bool() const { return (m > 0); }
  28.  
  29.         T& operator *()
  30.         {
  31.             static T e = 0; // this could be removed
  32.             if (m <= 0) // if someone tries to extract data from an empty vector
  33.                 return e; // instead of throwing an error, we return a dummy value
  34.  
  35.             m--;
  36.  
  37.             if (--p < 0)
  38.                 p = MaxSize - 1;
  39.  
  40.             return r.m_vector[p];
  41.         }
  42.     };
  43.  
  44.     decltype(auto) begin() { return m_vector.begin(); }
  45.     decltype(auto) end() { return m_vector.end(); }
  46.  
  47.     DummyIterator get_dummy_iterator()
  48.     {
  49.         return DummyIterator(*this);
  50.     }
  51. private:
  52.     std::vector<T> m_vector;
  53.     int m_pos = 0;
  54. };
  55.  
  56. template<typename T, size_t S>
  57. void show(TopN<T,S>& t)
  58. {
  59.     for (auto it = t.get_dummy_iterator(); it; )
  60.         std::cout << *it << '\t';
  61.  
  62.     std::cout << std::endl;
  63. };
  64.  
  65. int main(int argc, char* argv[])
  66. {
  67.     TopN<int,10> top10;
  68.     for (int i = 1; i <= 10; i++)
  69.         top10.push_back(5 * i);
  70.  
  71.     show(top10);
  72.  
  73.     top10.push_back(60);
  74.     show(top10);
  75.  
  76.     top10.push_back(65);
  77.     show(top10);
  78.  
  79.     return 0;
  80. }
  81.  
Success #stdin #stdout 0s 3412KB
comments (?)
stdin
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Standard input is empty
stdout
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50	45	40	35	30	25	20	15	10	5	
60	50	45	40	35	30	25	20	15	10	
65	60	50	45	40	35	30	25	20	15
https://ideone.com/SLSNpc
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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