This one felt pretty comfortable to interview with — slow pace, none of that being-chased-the-whole-time feeling. Each round was an hour, and in some rounds close to half the time was just chatting. The problems were medium-to-easy, but they really like steering things toward object-oriented design and code design — the questions here are different from what other companies ask.
A quick note: I'm writing the problem numbers as a coded homophone (a trick some posters here use), so I'll just spell out what each one actually decodes to.
Round 1
The interviewer was a veteran engineer with over a decade of experience. He spent the first fifteen minutes going deep on a project from my resume — he really wanted to know exactly what I was responsible for in it.
The problem decodes to LeetCode 236: Lowest Common Ancestor of a Binary Tree — given two nodes in a binary tree, find their lowest common ancestor.
Standard recursion: search the left and right subtrees, and if both sides return a node, pass the current node up; if only one side has a result, pass that one up. After I finished, he didn't rush into follow-ups. Instead he asked: "What does your function return if one of the two nodes isn't actually in the tree?"
That question hit the nail on the head. The standard implementation, in that case, returns whichever node does exist — but the semantically correct answer is null, because the common ancestor doesn't exist. I said that to fix it you'd need to track, during the recursion, whether each of the two nodes was actually found, and make the final judgment call at the top level. He had me write out the corrected version.
He also asked what I'd do if the nodes had parent pointers. I said that degenerates into finding the intersection of two linked lists: walk each node up to the root to get its depth, have the deeper one walk up the difference first, then walk both up together until they meet. No recursion, O(1) space.
My takeaway from this round: he doesn't care whether you can write it. He cares whether you know under what conditions what you wrote is actually correct.
Round 2
The problem decodes to LeetCode 31: Next Permutation. Given a sequence of numbers, rearrange it in place into the next lexicographically greater permutation, or into the smallest permutation if it's already the largest.
This isn't hard, but it's very easy to get wrong. I talked through the rule first: scan right to left to find the first descending position i, then scan right to left again to find the first position j where the value is greater than arr[i], swap them, then reverse everything after i.
The interviewer had me trace [1,3,5,4,2] by hand first (on a shared doc, really) to confirm the rule was right before letting me code it. He didn't say a word while I traced it through — just waited for me to finish on my own.
Once I wrote the code, the test cases he ran were [3,2,1] (already the largest, should become [1,2,3]), [1,1,5], and a single-element case. The second one was interesting because of the duplicate — when looking for j you have to find the "first strictly greater" element, not "first greater than or equal," or the swap ends up in the wrong order.
The follow-up was how to write the previous permutation. I said you just flip every comparison operator — the logic is fully symmetric. He said a lot of people re-derive the whole thing from scratch at this point, when there's no need to.
Round 3
This round barely had any coding — it was almost entirely about design.
There was a warmup problem first, decodes to LeetCode 102: Binary Tree Level Order Traversal. BFS, record the size of each level, done pretty quickly.
Then he steered it into design: "Say we want to build a generic tree-traversal utility that supports pre-order, in-order, post-order, and level-order, and also lets the caller do its own thing at each node it visits — how would you design it?"
My answer: separate "how to walk" from "what to do once you get there." Make the traversal strategy a set of different implementations, and pass the visit logic in through a callback or a visitor interface. That way, adding a new traversal order doesn't require touching existing code, and adding new processing logic doesn't require touching the traversal code either.
He followed up with a few more:
What if the caller wants to stop the traversal partway through? — the callback's return value can carry a signal, and the traversal engine exits early when it sees it.
What if the tree is huge and traversing it all at once blows the memory budget? — switch to an iterator with lazy evaluation, handing the caller one node at a time on demand. He had me explain how you'd implement an in-order iterator with a stack.
What if you need to support parallel traversal? — I said subtrees are independent of each other, so you can partition work by subtree, but the caller's callback has to be thread-safe, and that constraint needs to be spelled out clearly in the interface documentation.
This was the most valuable round of the whole loop, in my opinion — a lot closer to actual day-to-day work than grinding LeetCode. My advice for anyone interviewing here: spend some time beforehand being able to explain a few common design patterns in your own words, rather than reciting definitions.
Round 4 — Design
The problem was to design an internationalization (i18n) system for a product's text. The product ships in dozens of countries, and every piece of copy in the UI needs to display in the right language for the user's region.
This one leans toward architecture and API design, not the usual distributed-systems playbook.
I clarified a few things first: how many languages need to be supported, how often the copy changes, whether we need to support switching languages at runtime without a restart, whether translation is done by humans or has a machine-translation fallback, and whether there are cases where behavior needs to vary by region rather than just by language (e.g. English in the US and English in the UK use different date formats).
My proposal had two layers:
Storage layer. One resource set per language, where the key is a semantic identifier (like checkout.button.confirm) and the value is the copy in that language. Never use the English source text as the key, because the moment the English text changes, every language's mapping breaks. The interviewer nodded firmly at that one.
Access layer. A single interface: input is a key plus the current locale, output is the copy. Internally it looks up the requested locale first, and if not found, walks up a fallback chain (zh-TW falls back to zh, which falls back to the default language), so there's always something to display.
Follow-up questions:
First, how do you handle copy with variables in it? Like "You have 3 new messages" — you can't just do string concatenation, because word order differs across languages. You need placeholders plus parameters, and you have to handle pluralization rules, since some languages have more than two plural forms.
Second, how does a copy update take effect? I said resources can be pushed from the server and cached on the client with a version number, checked on startup, so copy changes don't require a new release. He followed up: "What if the push fails?" I said you keep a built-in default resource bundle as a fallback.
Third, how do you catch missing translations? I said you validate at build time by comparing whether each language's resource set has all the same keys — missing ones either fail the build or get flagged. At runtime, any lookup that can't find a key should get logged and reported.
Fourth, what if the translated text is longer and breaks the layout? I didn't answer this one well — I only said you need to leave room for flexibility. Thinking back, I should have brought up pseudo-localization testing.
Round 5
This one was with a manager, no coding.
Questions asked: what's something you've done recently that you're most proud of; has there been something you pushed for that others weren't sold on; what's the most frustrated you've felt at work; how do you work with product managers; where do you want to be in the next two or three years.
None of the questions were tricky, and he didn't dig in hard on any of them — it felt more like he was checking whether we'd get along. I was pretty relaxed about it, and we ended up talking about some non-technical stuff too.
The only one that got slightly more serious was "the most frustrated you've felt." I talked about a project I worked on for a long time that never shipped, and focused on what I learned from it — validate requirements up front, don't build the whole thing head-down and then go ask users if they actually want it.
A few takeaways:
- Slow pace, so you can actually finish your thoughts. You don't have to race the clock like at other companies — you can lay out your reasoning at your own speed, and the interviewers are willing to wait.
- The problems aren't hard, but they will ask "under what conditions does your solution actually hold?" That LCA problem in round one is the textbook example — being able to write it is just the passing grade.
- Object-oriented and code design is the real focus. There's a whole round that's almost entirely about interface design, extensibility, and separation of responsibilities — that's what actually separates candidates, more than the algorithms do.
- The design round might not be a distributed-systems question. Mine was internationalization — architecture and API design. The usual distributed-systems talking points don't apply, so when you prep, don't only aim at distributed systems.
- The behavioral round is relaxed. It felt more like a fit check than a grilling, so there's no need to be too tense.
Wishing everyone finds the right fit.
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