Just finished my Costco software engineering loop and I want to document the coding interview and online assessment in detail because I was flying blind going in.
Quick background: new grad, applied to their e-commerce engineering team in Issaquah, WA.
Online assessment (first technical filter):
Got it via HackerRank. Two coding problems, 90 minutes total. One was array manipulation (medium difficulty by LeetCode standards), one was more of a string parsing problem. Both had hidden test cases. No system design in the OA. Felt like a standard early-filter OA, not tricky.
Turnaround was weird. I submitted and heard nothing for 11 days. Then a recruiter called and said I was moving to the phone screen. I assumed it had gotten lost.
Technical phone screen coding portion:
The hiring manager (not the recruiter) ran this. They shared a coding environment, asked me one problem, gave me the full 45 minutes for it. The problem involved designing a simple cache (LRU-style) which is... not an unusual interview question but it was stated in a Costco-specific context ("think of this like a high-traffic item lookup on our website"). Medium difficulty, maybe medium-hard.
Important: they asked me to walk through my approach before writing any code. I've heard this from multiple Costco candidates. Don't just start typing.
Onsite coding round:
One dedicated algorithms round, plus the debugging round that remoteswe42 mentioned elsewhere in this thread. The algorithms problem in my round was a graph traversal problem, BFS variant. Genuinely not hard but I was nervous and blanked on the queue initialization for 3 minutes which felt like 20.
Overall difficulty: easier than Google/Meta, comparable to mid-tier tech company interviews. I wouldn't grind LeetCode hards for this. Focus on data structures fundamentals and be ready to talk through your approach clearly.