(C++) std::prev_permutation

 

std::prev_permutation is an STL algorithm to obtain the previous permutation of a container.

 

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#include <algorithm> #include <iostream> #include <iterator> #include <vector> int main() {   //Create a std::vector   std::vector<int> v;   v.push_back(1);   v.push_back(2);   v.push_back(3);   //Display std::vector   std::cout << "Initial v: ";   std::copy(v.begin(),v.end(),std::ostream_iterator<int>(std::cout," "));   std::cout << '\n';   //Obtain the next permutation   while(std::next_permutation(v.begin(),v.end()))   {     //Display std::vector     std::cout << "Next permutation: ";     std::copy(v.begin(),v.end(),std::ostream_iterator<int>(std::cout," "));     std::cout << '\n';   }   //Sort and reverse the std::vector   std::sort(v.begin(),v.end());   std::reverse(v.begin(),v.end());   //Display std::vector   std::cout << "Reverse-sorted v: ";   std::copy(v.begin(),v.end(),std::ostream_iterator<int>(std::cout," "));   std::cout << '\n';   //Obtain the previous permutation   while(std::prev_permutation(v.begin(),v.end()))   {     //Display std::vector     std::cout << "Previous permutation: ";     std::copy(v.begin(),v.end(),std::ostream_iterator<int>(std::cout," "));     std::cout << '\n';   } }

 

Screen output:

 

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Initial v: 1 2 3 Next permutation: 1 3 2 Next permutation: 2 1 3 Next permutation: 2 3 1 Next permutation: 3 1 2 Next permutation: 3 2 1 Reverse-sorted v: 3 2 1 Previous permutation: 3 1 2 Previous permutation: 2 3 1 Previous permutation: 2 1 3 Previous permutation: 1 3 2 Previous permutation: 1 2 3