went through microsoft's coding loop for a senior backend role earlier this year. sharing format and difficulty because the OA changed a bit and a lot of the prep guides are from 2023-2024.
the online assessment (OA)
if you apply through the portal for most swe roles, you'll get a HackerRank-style OA first. two coding problems, 90 minutes total. mine were: a medium array/sliding window problem a medium-hard graph BFS with a twist (tracking visited states that included a secondary condition)
no system design, no behavioral in the OA. pure coding. the difficulty felt like solid leetcode medium to medium-hard. i don't think i saw an 'easy' in the OA based on what friends have described either.
the coding round in the actual loop
if you pass the OA, you get into the loop. there's usually one dedicated coding round in the onsite (sometimes two if you're senior). the format is different from the OA: you code live in a shared editor (they seem to use their own internal tool, not coderpad). the interviewer can see you type in real time.
my problem was a tree traversal with some additional logic. medium difficulty. but here's the thing: they care a LOT about whether you can communicate while you code. i narrated my thinking out loud and the interviewer engaged with it. friends who went silent and just coded said the vibe was awkward and they got lower scores even when the solution was correct.
what i'd prep leetcode mediums. probably 80 of them at minimum before feeling ready. practice talking out loud while solving. this is underrated. know your time/space complexity cold. they WILL ask. know one clean solution pattern per problem type: two pointers, BFS/DFS, sliding window, dp (simple knapsack-style)
they're not as leetcode-hard-obsessed as google in my experience. but they do want clean, readable code, not just a solution that passes test cases.