Most of the time I got the wrong anwers on hidden test cases like Wrong Answer on 91 test case (Test 2) or 2000 test case (Test 7) etc.

Sometimes after trying all possible corner test cases and some random test cases I am not able to find which type of test case give the wrong answer.

I will highly grateful to you if you can give me some ideas which are really helpful to find those hidden test cases.

Thank You.