But you can't do that in 2 countries at once.
Obviously this assumes that given a range of dates, the number of days is calculated as inclusive of the date of ingress and egress.
USCIS will count the day that an applicant departs from the United States and the day he or she returns as days of physical presence within the United States for naturalization purposes.[1]
As long as the other country counts it the same way, you could spend 6 months in two countries and end up fulfilling the physical presence requirements in both.
[1]http://www.uscis.gov/policymanual/HTML/PolicyManual-Volume12...
They do well with this when it comes to tax, I don't see why they wouldn't do well just because it's a question of citizenship.
No, they don't, because it's based on border crossings recorded in your passport, not something trivial like rent payment records.
This was not as simple as counting the stamps in my passport, and I didn't really know whether the Home Office had any other way of tracking me. It took several days for me to compile the complete list.
As an example, fly London to Belfast, rent a car and drive to the Republic of Ireland. No stamp in the passport.
A few times traveling to the European mainland, other than by air, resulted in a lack of either arrival or departure stamps.
My passport was never stamped on departure from the UK.
Now I have British citizenship, I regularly travel across multiple EU borders and no crossing is recorded in my passport.
My British passport, although two years old, does not have a single stamp in it, and I've been resident in a different EU country for the past year.