Fairly random because the questions you get asked are based on the interviewer/team. It's difficult, but not impossible if you get lucky.
For example, I didn't get asked system design during my onsite, and the phone interview was LeetCode Easy. However, the final leadership round did have a LeetCode Hard question that took me some time.
Some questions marked with "Citadel" on LC.
The following metrics were computed from 18 interview experiences for the Citadel Software Engineering Intern role in United States.
Citadel's interview process for their Software Engineering Intern roles in the United States is extremely selective, failing the vast majority of engineers.
Candidates reported having very good feelings for Citadel's Software Engineering Intern interview process in United States.