What is the most difficult computer science course you had to take in university?

Software Testing it's hardest subject for me

My study was Electronic and embedded systems, I think Embedded system was the hardest subject specialy embedded system fonction in real time, the concept of real time ,#rtos,#osa,#real-time.

My speciality is physics, most of our computer science courses where not difficult, but I remember my computer science students colleagues complaining about compilers science.

I think system analysis and design was the most difficult subject for me

Programming and Algorithm related subjects were tough for me. Then gradually I  overcame it...

Programming for Computer Networks was the toughest subject I have ever studied. It wasn't user friendly

Although, my study was telecom but I think AI which stand for Artificial Intelligent was the hardest subject.

1. Theory of Computation, 2. Image Processing and Computer Vision