Running this code locally gives Runtime Error on test 3 due to this:

s.erase(s.find(cnt));

Which I replaced by this:

auto itr = s.find(cnt);
    if (itr != s.end())
        s.erase(itr);

And it passed all test.

It took me less than a minute to figure out that deletion might be causing RE.

But during the contest, I spent more than an hour thinking about why it was giving TLE.

Is this normal behaviour on Codeforces compilers or is it a bug. If it's normal, then how do we deal with such verdicts (a TLE which actually is just a RE)?