We need to bring 1 friend to be the second test subject.

Both test subjects take 2 pills at the same time: A,B and B,C.

If both are affected, the jar is B.
If neither are affected, the jar is D.
Otherwise the one affected reveals it to be either A or C.

even with the solution this problem make no sense to me.
How can the solution to n=4 is 1 ?
they can only do 1 test since he have 35 minutes ?

just maths, boring, totally useless.
The only thing I learn here is that I hate maths more.

Really painful you don't know witch test is wrong in swift.
Impossible to learn and progress.