fork(3) download
copy 
  1. #include <iostream>
  2. #include <set>
  3.  
  4. typedef  std::pair<int, int> PairInt;
  5.  
  6. namespace std
  7. {
  8. template<>
  9. bool operator < (const PairInt& l, const PairInt& r) 
  10. {
  11.     //swap only if they're unequal to avoid infinite recursion
  12.     if (l.first != l.second) 
  13.     {
  14.          //swap elements, considering your special case
  15.           if (l.first == r.second && l.second == r.first)
  16.              return l < PairInt(r.second, r.first); //call again!
  17.     }
  18.  
  19.    //actual comparison is done here
  20.    if ( l.first != r.first )
  21.         return l.first < r.first;
  22.    else 
  23.         return l.second < r.second;
  24. }
  25. }
  26.  
  27. int main()
  28. {
  29.     std::set<PairInt> intSet;
  30.     intSet.insert(PairInt(1,3));
  31.     intSet.insert(PairInt(1,4));
  32.     intSet.insert(PairInt(1,4));
  33.     intSet.insert(PairInt(4,1));
  34.     for(auto it = intSet.begin(); it != intSet.end(); ++it)
  35.            std::cout << it->first << "," << it->second  << std::endl;
  36. }
Success #stdin #stdout 0s 2964KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
1,3
1,4
https://ideone.com/yQ2l1
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!