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  1. #include <vector>
  2. #include <stdexcept>
  3. #include <algorithm>
  4.  
  5. template<class iterator_type>
  6. class combination_generator {
  7.     iterator_type first, last;
  8.     std::vector<bool> use;
  9.     unsigned r;
  10.     typedef typename std::iterator_traits<iterator_type>::value_type element_type;
  11. public:
  12.     combination_generator(iterator_type first_, iterator_type last_, unsigned r_) : first(first_), last(last_) , r(r_)
  13.     {
  14.         use.resize(std::distance(first, last), false);
  15.         if (r > use.size())
  16.             throw std::domain_error("can't select more elements than exist for combination");
  17.         std::fill(use.end()-r, use.end(), true);
  18.     }
  19.     template<class output_iterator>
  20.     bool operator()(output_iterator result) 
  21.     {
  22.         iterator_type c=first;
  23.         for (unsigned i = 0; i<use.size(); ++i,++c) {
  24.             if (use[i]) 
  25.                 *result++ = *c;
  26.         }
  27.         return std::next_permutation(use.begin(), use.end());
  28.     }
  29. };
  30. template<class iterator_type>
  31. combination_generator<iterator_type> make_combination_generator(iterator_type first, iterator_type last, unsigned r)
  32. {return combination_generator<iterator_type>(first, last, r);}
  33.  
  34. #include <string>
  35. #include <iostream>
  36. #include <iterator>
  37.  
  38. int main() {
  39.     std::string data[] = {"HELLO", "WORLD", "ALPHA", "BET"};
  40.     auto generator = make_combination_generator(data, data+4, 2);
  41.     std::ostream_iterator<std::string> it(std::cout, " ");
  42.     while(generator(it)) 
  43.         std::cout << '\n';
  44.     return 0;
  45. }
  46.  
Success #stdin #stdout 0s 3432KB
comments (?)
stdin
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Standard input is empty
stdout
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ALPHA BET 
WORLD BET 
WORLD ALPHA 
HELLO BET 
HELLO ALPHA 
HELLO WORLD
https://ideone.com/UpwKvC
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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