You can file the N-400 now - but you will most likely have to prove that you didn't leave the US to live elsewhere, that you only travelled temporarily even if it turned out to be longer than 6 months. You can google what evidence USCIS wants to see - some include evidence that your immediate family (spouse, kids) remained in the US when you were gone, that you didn't end your rental agreement/lease or sold your house, that you still filed your taxes, that you renewed your drivers license/ID if it expired, that you didn't quit your job, didn't sell your car, kept all your insurances (health, car, home etc).