I was attempting the following question 310D

Here is my submission that timed-out TLE

And here is my submission that was accepted AC

As you may have observed, the only change I made from the TLE code to AC code was

  it=lower_bound(s.begin(),s.end(),mp(lo,o));

to

  it=s.lower_bound(mp(lo,o));

where "it" is a set iterator.

Just changing this, the time on Test #11 was reduced from >3000ms to 264ms. Can any one shed some light on why this happened? Thank you.