11387 - The 3-Regular Graph/p11387.cpp

   1 #include <iostream>
   2
   3 using namespace std;
   4
   5 int main(){
   6   int n;
   7   cin >> n;
   8   while (n){
   9     //procesar caso
  10     if (n <= 3 || n % 2 == 1){
  11       cout << "Impossible\n";
  12     }else{
  13       int mitad = n / 2;
  14       cout << mitad * 3 << endl; // # of edges
  15       for (int i=1; i<n; ++i){
  16         cout << i << " " << i+1 << endl; //borde
  17       }
  18       cout << n << " 1" << endl; // cerrar borde
  19       for (int i=1; i<= mitad; ++i){
  20         cout << i << " " << i+mitad << endl;
  21       }
  22     }
  23     cin >> n;
  24   }
  25   return 0;
  26 }