Fortinet Embedded Software Engineer interview questions

I applied to Fortinet in 2019 for an Embedded Software Developer role via Linkedin. I tried to connect with an HR staff via linked and she sent me the online test some days later. There are two parts in the test: multiple choice questions and coding.

refered by a empoyee, got the interview after a remote programming test; it took about nealy 3 hours from the very beginning to end, it's a complete technical interview, no words about anything else; 3 engineers interviewed me, mainly two of them asked questions from data structure, C, C++, Linux. They asked question from simple to hard and gradually detailed into the code implementation, you did not only answer the question, you need to explain the answer why you think its right; they wouldn't change another question unless you can explain the answer totally clear or you just stucked and cannot say anything more.