I'm male. Imagine I arrive at a youth hostel where I'm the only Jew. It's a big house on a quiet residential street; the house has been converted into a youth hostel. There's a male-only dorm room. And, across the hallway, there's also a female-only dorm room. Assume that the doors to all the dorm rooms are unlocked.
If I recall correctly, Jewish law normally assumes that non-Jews are not "shomer negiah". And so, if I would stay the night, I think Jewish law would consider me to be the only shomer-negiah individual staying in the entire building. I'm not sure whether or not this would pose any halachic problem.
Chabad rabbi Nissan Dovid Dubov briefly discusses the matter of yichud (seclusion) together with a large group of non-Jewish men and women. For example, he writes:
A woman may not ride a bus on a deserted country road even though there are many non-Jewish men and women on the bus.
Do the laws of yichud allow me to sleep in the male-only dorm room?