PROBLEM LINK:https://codeforces.net/contest/1553/problem/B

my solution to this problem got hacked during the contest after it passes the pretests(4).I want to know is there a possibility suppose the hacker didnt hack my solution during the contest and in system testing my solution get accepted because the tests prepared for the question was not good enough or lets say it excludes the test case through which the hacker hacked.??

Also i want to know after somebody succesfully hack other solution do code forces add that particular hack test to their set of tests for system testing or code forces set of tests already has that test case covered.?? please answer

Thanks in advance