About 14 hours. From 10 AM to 12 PM.

It was a difficult problem on one of those algorithm practice websites, which I just couldn't let go of. I spent most of the time trying to micro-optimize and do the same (wrong) thing in different ways.

The next day, I managed to finish the problem in 2 hours using a different approach.

I learned a bunch of things from this:
- Algorithm analysis matters.
- If you spend too much time on a problem without taking longer breaks, you get stuck in a loop repeating the same mistakes.
- A fresh mind is significantly more productive and creative. Take a break, think about other things and let go of that mental baggage, you'll be surprised.