I think they would be using a command that is probably grep to compare two files:
One is our output file and Seond is there standard output file.
the would have to chage this some to increase user interactivity and to give him an idea about the percentage of the problem he had successfully understood.
In facts, this information gives you nothing , because you still will not know what do you do wrong
Best regards
DM
PS. Are you think, that information something like "73,15% correct" tell you more than you are wrong ?
If you really want to get Accepted, try to think about possible, and after that - about impossible ... and you'll get, what you want ....
Born from ashes - restarting counter of problems (800+ solved problems)