Hair drug test- getting clean?

So im a younger guy, 5'11 about 165 and ive been smoking everyday for probably about 2-3 years continously now. I usually dont smoke until after my classes and later in the day so i dont normally smoke more than a gram a day or a couple dabs. I have a drug test coming up at some point for an engineering job, not worried about getting pee tested as i will be clean urine-wise by the time i should be tested, the job wont start till january 2018 and so i wouldnt expect to be drug tested any earlier than december of this year (if you disagree please tell when you would expect a drug test for an engineering job starting in january) . I stopped smoking on 9/10, what should i do to make sure im clean for a hair test by then? I hear hair only grows 1.5 inches in 3 months but my hair has grown that much since my last haircut a month ago. Im more just looking for reassurance that i will be clean and some options to speed up the process to make sure i am clean as soon as possible. Any replies appreciated.