I think it would nice to have constraints added in the 30-Days challenge questions, similas as we do with problems from Weekly & Bi-Weekly contests. If not constraint, at least specify the time/space complexity the problem is aiming for, otherwise is hard for us to come up with the right solution. It is like coding the solution blind, since you are not sure whether it will pass or not until you actually submit the solution and see how large the input is.

My recommentation is, either add constraints, or even better, since those problems are accounting for interview practising, then just add an expected time complexity in there so people will know what the actual challenge is and would not expect an accepted if they do not come up with that specific time/space complexity solution.

Thanks in advance :)