.

You should never delete element in a range-based for loop. In the AC code, the element are deleted later after the for loop. If you still wanna delete element while iterating:

for(auto it = s.begin(); it != s.end(); ){
    if(/*delete condition here*/) it = s.erase(it); //return the next iterator
    else ++it;
}

I still prefer to delete outside the loop than delete inside the loop. From my experience, set is a magic data structure in C++, sometime you couldn't find where your code cause RTE without printing every possible variables, debugger can't help. So be careful, otherwise you will have a great time debugging hopelessly.