When I was in highschool there was an online competition every week.

So one week there was this very hard problem. I didn't knew how to solve this but I figured out that there is one answer per 10 tests.

I bruteforced easy tests and send program with different answers std::cout<<30<<endl; ... So I send like 500 different programs. Then I just combined correct result with size of test ;p. I use while true to figure size for every test ;p

I passed every test. Week later my solution was removed and I got very nice e-mail about what I did and how wrong It was to exploit platform.

I still managed to be in top 10 at then end of competition but It was mistake huge mistake

Ps. Competition was with very good prizes but still I am ashamed of myself for that.