If I am a cheater and have solutions to some problems, and for each solution, I read the code, understand it, and then write my own code from scratch based on the idea of the code I copied as if I came up with the idea myself, how can Codeforces catch me? How can the Codeforces system detect this type of cheating?

Hi MikeMirzayanov I have an issue with my 213400052 for problem D today. I passed the pretests, which consisted of 10 tests, but my code failed in test 7 during the system test due to a memory limit that I exceeded. I'm not sure what this means. Additionally, I submitted the same code 213422705 using the G++ 17 compiler and it was accepted, but when I used G++ 17 64 bit during the contest , I exceeded the memory limit. Can someone explain this to me? I don't think it's fair