On Topjohnwu's github, there´s a note about root any Samsung without recovery
Basically, extract the AP from stock firmware, copy it to phone, install magisk from xda forum, patch it, download the patched file to your pc and flash it using Odin.
You must fresh flash the entire ROM and the patched AP, userdata MUST be formatted (use CSC, not HOME_CSC)
Use it at your own risk, Knox wil be tripped and you could brick your phone.
Search the note into Topjohnwu´s github, Magisk section, Install and search for specific samsung section.
Be careful and enjoy rooting!