c++ sort keeping track of indices

Question

do you have some efficient routine for returning array with indices for sorted elements in a array? I think that some convenient way exists using stl vector. Do you have alr

Answer 1

For C++03, I think this guru of the week can help you :

namespace Solution3
{
  template
  struct CompareDeref
  {
    bool operator()( const T& a, const T& b ) const
      { return *a < *b; }
  };


  template
  struct Pair2nd
  {
    const U& operator()( const std::pair& a ) const
      { return a.second; }
  };


  template
  void sort_idxtbl( IterIn first, IterIn last, IterOut out )
  {
    std::multimap > v;
    for( int i=0; first != last; ++i, ++first )
      v.insert( std::make_pair( first, i ) );
    std::transform( v.begin(), v.end(), out,
                    Pair2nd() );
  }
}

#include 

int main()
{
  int ai[10] = { 15,12,13,14,18,11,10,17,16,19 };

  std::cout << "#################" << std::endl;
  std::vector aidxtbl( 10 );


  // use another namespace name to test a different solution
  Solution3::sort_idxtbl( ai, ai+10, aidxtbl.begin() );


  for( int i=0; i<10; ++i )
  std::cout << "i=" << i
            << ", aidxtbl[i]=" << aidxtbl[i]
            << ", ai[aidxtbl[i]]=" << ai[aidxtbl[i]]
            << std::endl;
  std::cout << "#################" << std::endl;
}

The original article is here.