I understood what the right solution should be. I think the test cases were not strong enough.
If you got an AC then your solution is likely to be wrong as the tester’s solution is. 
“Thank you for your detailed report. We apologize for the weak test data. After analyzing, we found that this does not disadvantage users who had correct answers too much, and hence we are keeping the contest rated. We will ensure that such issues don’t crop up again.”
This is the reply that I got for my email.
1 Like
Problem with super quick explanation’s latex:
Find largest value X, such that X is reachable while X+1 is not reachable, then all values up to X and values V which satisfy X < V \leq S and X \equiv V \pmod{2} are reachable, where S is sum of array.