I dealt with cigarette smokers in my last apartment, and that in itself was a pain in the ass. The last thing I want to smell when I get up first in the morning, is someone's goddamn smoke. But what could I do? I mean, you can't tell them to stop. They're within their rights. I was able to eventually solve the problem, but i wasn't terribly happy with the solution.
Basically, I sealed the cracks of my two doors leading to our shared hallways with duct tape. When I would open the door, it would peel away from the frame, sticking to the door. When I closed the door, I would run my fingers along the tape, sealing it back down to the frame. Pain in the dick to do it every time, but it kept the smell out. It worked.
You may be able to achieve similar results with some kind of rubber seal or gasket you can affix to the door in a similar fashion but, if you're looking for a cheap and easy fix, duct tape will do it.