I've never studied any computer science. So I've always passed over restricted-complexity questions, since I had no way of knowing the complexity of my code. Today, I decided to try and see whether I could change that. I read the tag description (as available on mobile, which I think is only the shorter part of it), which gave no info on how to find complexity, so Googled and found https://stackoverflow.com/q/9958299, which says there is no general way to find complexity. So how do I know the complexity of my code for a restricted-complexity question?
Ask in chat
Your best bet is to ask someone else. Learning to evaluate the asymptotic complexity of a program is a pretty standard subject in most college CS educations, so there will probably be a number of people in chat who can either walk you through evaluating the complexity or do it for you, although the latter may be more difficult if you're using an esoteric language.
For most small (<100 lines in a conventional language) programs, it's pretty easy to evaluate the complexity with some practice, so someone can often walk you through it.
As an aside, evaluating complexity automatically is an ongoing research question in the programming languages world. I know some people who are working on it at my university. The best efforts cover a fair number of cases, but aren't all that general, and require you to write your program in their language. For the time being, human evaluation is typically the most effective.