Done

Honestly i figured I know what you mean, I've removed my explaination for it. I guess you can figure it out on your own.

I thought giving advice wasnt generally a bad idea, what do you think should I remove from my description?

OP solved it , closing

enabled, updated to new test framework as well

This comment is stupid. Numerical integration methods have different accuracies. Euler method is O(h) while RK4 is O(h^4). (Note that there are even more accurate methods, having worse overhead and more error-prone to implement.) You'd literally only use Euler method if you don't care about numerical accuracy of your results.

@rge123 It's been a long time since I wrote this kata, but IIRC there shouldn't be a case where a Deny will occur for a nation that has not already been allowed beforehand. But to be on the safe side I'd recommend assuming that this type of example may come up and taking that possibility into account in your solution.

Yep

I was also confuzed about this at first, but it's actually stated in the description: "list of nations [...] whose citizens may enter (begins empty, before the first bulletin)". So, all nations are denied by default.

"Allow" doesn't override missing vaccines or other problens (if a guy has any problem, he's rejected)

See a note at the bottom of the description. Calculating the full list even for n==200 is a transcomputational problem.

fixed - thank you for letting me know ^v^

The 1e-9 precision is required to ensure the exact RK4 method is used. Not to be close to the real solution.