Nice post. What tools do you use to understand which line of the code is creating a bottleneck? For instance, the "if statement has too many false positives" in Solution #4. Do you locate these bottlenecks simply by manual inspection of the code?
A lot of these are actually pretty easy to spot with tools like gcov. To determine false positives, we can just look at how many times each "if" statement was hit, and compare those to the final count.