Today I was attempting to hack this submission for 2061B. In this solution, the code uses s1.count(x) inside the input-reading loop. Since the time complexity of multiset's count function is $$$O(\log n + k)$$$, where $$$k$$$ is the number of occurrences of the element, the code's time complexity should become $$$O(n^2)$$$ if all elements $$$a_i$$$ are set to $$$1$$$.

However, when I submitted the hack, this code only took 109 ms. Local testing showed that it indeed results in a TLE without -O2, but runs very quickly with -O2 enabled. Does this indicate that the compiler optimizes std::multiset.count() when it is used as boolean?