Went through HP's coding process twice in the past year (once for a frontend role, once for a full-stack position on a different team). The OA and live coding rounds are different enough that I'll break them out separately.
Online Assessment (OA)
The OA I got via HireVue came before any human conversation. It was timed, 90 minutes, 3 problems. Problem 1: easy warmup. Array manipulation, basically checking if you can write clean code. Mine was a variation of finding contiguous subarray sums. Problem 2: medium difficulty. Graph or tree problem. Mine was a shortest path variant on an unweighted graph. Nothing exotic. Problem 3: medium-hard. Second time I took it I got a dynamic programming problem (grid traversal with constraints). First time it was string parsing.
Language choices were broad: Python, Java, C++, JavaScript. I used JavaScript since I was applying for a frontend role and wanted to be consistent.
No behavioral questions in the OA, which was a relief. Some companies mix those in.
Live Coding Round (phone screen / virtual onsite)
For the full loop, I had two live coding rounds. One was collaborative (interviewer was chatty, gave hints, felt almost pairing-like). The other was more formal. Both were LeetCode medium in difficulty. I did not see a single LeetCode hard across either loop.
Topics I saw across both experiences: arrays, hash maps, binary search, BFS/DFS, basic DP. No system design in the coding rounds, no bit manipulation, no segment trees. Pretty classical.
Timing and format
Each live round was 45-50 minutes. About 5 minutes of intro, 30-35 minutes of problem-solving, 10 minutes of my questions. They used CoderPad both times.
One thing worth knowing: interviewers vary a lot in how much they guide you. One interviewer jumped in when I was stuck and gave a meaningful hint. The other stayed silent for a long time. I think it's the luck of who you get, not a consistent policy.
For prep: Grind mediums, get comfortable talking while coding, and know your time/space complexity cold. I think they filter more on clarity of thought than on whether you nail it in the first 10 minutes.