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  1. #include <iostream>
  2. #include <map>
  3. #include <vector>
  4.  
  5. template <typename T>
  6. struct ChooseKfromN{
  7.     T   mbegin;
  8.     T   mend;
  9.     std::vector<T> combo;
  10.     ChooseKfromN(T first,T last,int k) : mbegin(first),mend(last),combo(k,first) {}
  11.     bool increment(){
  12.         for (auto it = combo.begin();it!=combo.end();it++){
  13.             if (++(*it) == mend){
  14.                 if (it != combo.end()){
  15.                     auto next  = it;
  16.                     next++;
  17.                     auto nexit = (*next);
  18.                     nexit++;
  19.                     std::fill(combo.begin(),next,nexit);
  20.                 }
  21.             } else  { return true;}
  22.         }
  23.         std::cout << "THIS IS NEVER REACHED FOR A MAP !! \n" << std::endl;
  24.         return false;
  25.     }
  26.     typename std::vector<T>::const_iterator begin(){ return combo.begin();}
  27.     typename std::vector<T>::const_iterator end()  { return combo.end();}
  28. };
  29.  
  30. template <typename T>
  31. ChooseKfromN<T> createChooseKfromN(T first,T last,int k) { return ChooseKfromN<T>(first,last,k); }
  32.  
  33.  
  34. int main(){
  35.     std::vector<std::string> xx = {"A","B","C"};
  36.     //std::map<int,int> xx;
  37.     //xx[1] = 1;
  38.     //xx[2] = 2;
  39.  
  40.     auto kn = createChooseKfromN(xx.begin(),xx.end(),2);
  41.     int counter = 0;
  42.     do {
  43.         for (auto it = kn.begin();it != kn.end();it++){
  44.             std::cout << (**it) << "\t";
  45.         }
  46.         std::cout << "\n";
  47.         counter++;
  48.     } while(kn.increment());
  49.     std::cout << "counter = " << counter << "\n";
  50. }
  51.  
Success #stdin #stdout 0s 16064KB
comments (?)
stdin
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Standard input is empty
stdout
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A	A	
B	A	
C	A	
B	B	
C	B	
C	C	
THIS IS NEVER REACHED FOR A MAP !! 

counter = 6
https://ideone.com/p5Zh9O
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
secret

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