Done.

Perhaps the intended complexity should be hinted in the description.

No, IIRC the mapping between a letter and a digit is always 1:1.

"Each unique letter may only be assigned to one unique digit"
Just to clarify, a number can be assigned to multiple letters, right? For example, can A and B can both have the value 5?

The intended solution should have O(logn) complexity.

Is brute force the intended solution for this problem, or is there some clever trick needed to solve this?

Oh, I must have misread the problem. Thanks!

This is already explicitly stated in the Description, under Conditions for passing inspection:

• If entrant is a foreigner, a grant_of_asylum or diplomatic_authorization are acceptable in lieu of an access_permit. In the case where a diplomatic_authorization is used, it must include Arstotzka as one of the list of nations that can be accessed.

Can there be some information about diplomatic authorizations? From what I can gather from the test cases, a diplomatic authorization is just a sort of "replacement" for an access permit. Is this true? If so, please consider making it explicit in the problem statement.

Yes, that is allowed. In fact, a valid solution for the example test in the Description is ['NNE','EES','','SS']

Hey another question- are we allowed to just do nothing for an interval?
Something like ['NEESS', '', NE]

No guarantees.

Is it guaranteed that you won't visit the same place twice for the optimal solution?