struct interval { int s; int e; }

struct comparator {
  bool operator(const interval& i1, const interval& i2) const {
    int i=i1.e-i2.e; // higher ends placed last
    if(0==i) { // higher length/lower starts will be higher
      i=i2.s-i1.s;
    }
    return i<0;
  }
}

int count_intervals(std::vector<interval>& sets) {
  if(sets.empty()) return 0;

  comparator comp;
  std::sort(sets.begin(), sets.end(), comp);

  /* if you need the solution as well, use a stack */
  // std::stack<std::vector> solution;
  interval& stack_top=sets[sets.size()-1]; // solution.push(stack_top);
  int count=1; // jave at least
  for(int i=sets.size()-2; i>=0; i--) {
    interval& curr=sets[i];
    if(curr.s > stack_top) { // a better one, lets more room in front
       stack_top=curr; // solution.pop(); solution.push(curr);
    }
    else if(curr.e < stack_top.s) {
      stack_top=curr; // solution.push(curr);
      count++;
    }
  }
  // if you need the solution, arrange the params of the function to return it
  return count;
}