I discovered https://highload.fun the other day and it is my new obsession. My first naive solution here scored 309,783. After a day or two of finding ways to shave off execution time I finally claimed the top spot on the list.
I might try them in the other languages, but honestly C# is a challenge that I like. Especially as the site (currently) doesn't support unsafe code. Naturally it means the other three are far more competitive and have much lower scores.