How to root Samsung Galaxy Alpha SM-G850A?
You may need to unlock the bootloader before doing this process. Here is tutorial.

As you mentioned above about odin , it means you know how to work with odin. Now just download this CWM recovery file and flash it using Odin.
Now download this flashable SuperSu zip.. Move this SuperSu zip to your sd card. Now you have to boot in recovery mode after flashing CWM recovery. In recovery mode install this zip file and reboot.

This is the best way to root any android.