On CF 256 Problem A, I use lower_bound to binary search. However, I've found that using std::lower_bound(set.begin(), set.end(), val) makes the solution blow up, resulting in TLE (>3000ms), while using set.lower_bound(val) works perfectly fine (~300ms).

AC (358ms): 48402685 TLE (3000ms): 48402684

It appears, then, that std::lower_bound(set.begin(), set.end(), val) is not actually binary searching. What is causing this behavior?

Thank you!