Got a Walgreens OA last month for a software engineer role (entry-level/junior tier, their early career program). Sharing because I basically found nothing useful when searching for this before I took it.
The OA came through HackerRank, link sent about 3 days after the recruiter screen. I had 5 days to complete it, 90-minute window once started.
Format: 2 coding problems 1 multiple-choice / short answer section on SQL and general CS concepts Time limit: 90 minutes for the whole thing
Coding problems: Mine were both what I'd call easy-medium on LeetCode. The first was a string manipulation problem (finding the longest substring meeting certain conditions). The second was an array problem involving counting elements that satisfied overlapping criteria. Nothing that required advanced graph or DP knowledge at this level.
The SQL section had about 8 questions. Mostly SELECT + JOIN + GROUP BY territory. One window function question that tripped me up briefly. They weren't asking you to write the query, just pick the right option from 4 choices, which made it more of a reading comprehension exercise than a SQL skills test.
CS concepts section: Basic data structures (when to use a hash map vs list vs set), one recursion question, one about REST vs SOAP (I guess they still ask this?). Nothing deep.
Timing: I finished in about 65 minutes. The coding portion took longest. I'd say if you're comfortable with easy-medium Leetcode and have done any SQL, you're fine.
Difficulty comparison to other OAs I've done: easier than Amazon's SDE1 OA, roughly similar to a mid-tier company's screening. Not a filter that weeds out a ton of prepared candidates, more of a sanity check.
One thing: I got dinged slightly in recruiter feedback for not writing comments in my code. Apparently the evaluators look at code quality, not just correctness. Add comments.
Passed the OA and moved to a phone screen. Happy to answer specifics.