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Practice coding, system design, behavioral, and project questions for frontier AI roles.
Every question has a public brief with the task, constraints, and follow-ups. Labels describe interactive practice access.
Reported interview periodNot available
Two people edit one note and both need to see the last line that was saved.
Practice focusSystem design round. Two people share one note. Say where the note is stored. Say what both people see when they save the same line. Say what the second person sees when their save does not land. Stop when a third person can only read.
Reported interview periodNot available
A hiring-manager conversation about one team and one project you already owned.
Practice focusHiring-manager round. Stay on one project you owned. Name the team and the problem they had. Say what you decided and who else had to agree. Give one measurement from the month after. The interviewer asks what you would stop if that team were half its size. Name the stop, and the sentence you would use to tell them. Do not switch projects.
Reported interview periodNot available
What you would cut if the team lost half its people.
Practice focusHiring-manager round. Half the team is gone next month. Stay on one project. First, list the work you stop and the work you keep, with the reason for each. Then the interviewer asks who you tell first and what you say in the first minute. Include the sentence, and include one promise you will not make. Then they ask what you would measure two weeks later to know the cut was the right one. Answer with one measurement.
Reported interview periodNot available
Two people edit one note and need to see who wrote the last line.
Practice focusSystem design round. Two people share one scratch pad during a review. Start by listing what must be true: neither person loses a line, and both can point at who wrote the last line. Place the note in one store and give each save a version. Walk the case where both save the same version. Then the network drops the second save: the first person must not think the second line landed. Then add a third reader who only watches. Say what that reader sees, what you store, and what you would not build for a note this small.
Reported interview periodNot available
Where a design failed after launch, what you measured, and what you changed.
Practice focusProject round. One system, after launch. Start with the design you intended. Then the failure, including who felt it. Then the measurement, including the unit and the window. Then the change. The interviewer asks what you left alone and why. Answer with one thing you refused to change. Then they ask how you would know the failure had returned. Point at the same measurement. Do not switch projects.
Reported interview periodNot available
Explain one result you trust, what would falsify it, and what was not shown.
Practice focusResearch round. Explain one result you trust, in four parts: the claim, the comparison, the evidence, and the limit. The interviewer asks what single observation would make you drop the claim. Answer with that observation, not a general doubt. Then they ask what the authors did not show. Name one missing comparison. Then they ask whether you would ship a product on this result today. Answer yes or no, and the reason is the falsifier you already named.
Reported interview periodNot available
During a timed test, mark seats as taken and report the first free seat.
Practice focusOnline assessment. A row of seats is numbered from 1. Implement take, which marks a free seat as taken and fails if that seat is already taken. Implement first free, which returns the lowest numbered free seat, or reports that the row is full. Then the test adds a second row and asks you to search the first row before the second. Write both functions and one example of a full row.
Reported interview periodNot available
On a phone screen, merge two sorted name lists and keep one copy of a shared name.
Practice focusPhone screen. You are given two lists of names. Each list is already in alphabetical order. Return one list in that order. A name that appears in both lists appears once. An empty list stays empty. Then the interviewer adds a name that appears twice in the first list and asks you to keep one. State that rule, then write the function.
Reported interview periodNot available
Keep the notes from a shift and return them in the order they were written.
Practice focusCoding round. A shift collects notes. Add a note for a person, and reject a blank note. Return every note in the order it was written. Then return the notes from one person only, still in that order. Write the functions and one example with two people.
Reported interview periodNot available
You own a useful model feature with a fixed launch date and one unresolved safety concern. Explain the concern, bound the plausible harm, choose what ships, and define the evidence required before expanding acc…
Practice focusPreparation - Write the user or stakeholder, the constraint, and the decision in one sentence each. - Choose one measurement or observable fact that can support the answer. - Name one alternative and the reason it was not selected. Review checklist 1. Did I state the concrete constraint before describing the solution? 2. Did I separate my own decision and work from the team's work? 3. Did I name evidence or a measurement rather than relying on confidence? 4. Can I answer every follow-up without changing the original facts? Staged follow-ups 1.…
Reported interview periodNot available
Walk through a system you made more reliable after a serious failure. Cover the failure boundary, your diagnosis, the design change you owned, the rollout, and the evidence that recovery improved.
Practice focusPreparation - Write the user or stakeholder, the constraint, and the decision in one sentence each. - Choose one measurement or observable fact that can support the answer. - Name one alternative and the reason it was not selected. Review checklist 1. Did I state the concrete constraint before describing the solution? 2. Did I separate my own decision and work from the team's work? 3. Did I name evidence or a measurement rather than relying on confidence? 4. Can I answer every follow-up without changing the original facts? Staged follow-ups 1.…
Reported interview periodNot available
Turn an unknown biased bit source into balanced choices, a sampled load estimate, and isolated concurrent batches.
Practice focusYou receive a hardware source raw bit() that independently returns 0 or 1 with one stable but unknown probability of returning 1 . The probability is strictly between zero and one, and no other random source is available. Implement the following four functions. Requirements 1. Extract balanced bits Read the raw source in fresh pairs. Discard pairs whose values match. For the first pair whose values differ, return its first value. A scripted source raises EOFError when exhausted; let that exception propagate, including for a partial pair.…
Reported interview periodSep 2025–Aug 2026
You are given a correct but slow numerical kernel, representative inputs, a correctness checker, and a benchmark. Improve its measured throughput without changing its output contract.
Practice focusAssumption: the precise production kernel and hardware contract are unavailable in this preparation version. Begin by implementing and optimizing compatible rectangular matrix multiplication over numeric arrays: Reject incompatible or ragged inputs. Preserve numerical correctness within the stated tolerance and do not special-case benchmark inputs. For this preparation interface, matrices are nonempty rectangular lists with nonempty rows and finite real entries (booleans are not numbers).…
Reported interview periodJul 2025–Aug 2026
Build utilities for converting between stack observations and call events. Stack frames are ordered outermost to innermost.
Practice focusFor an event stream, push on enter / start , pop on exit / end , record the stack after each event, and run-length encode adjacent identical stacks. For sampled stacks, compare adjacent samples using their longest common prefix. Emit removed frames as end events from innermost outward, then emit added frames as start events from outermost inward. Use the new sample's timestamp and leave frames in the final sample open. Samples have ts and stack fields; events emitted from samples have name , kind ( start or end ) and ts .…
Reported interview periodSep 2025–Aug 2026
You are given an LLM client whose responses may contain text blocks or one or more tool-call blocks. Build an agent that answers a user question by repeatedly calling the model, executing requested tools, retur…
Practice focusAssume two tools are available: a stock-price lookup and a shares-outstanding lookup. A question may require one lookup, several independent lookups, or combining results such as market capitalization. Requirements - Preserve the complete conversation history, including assistant tool calls and matching tool results. - Execute every tool call in a response; do not silently discard parallel calls. - Match each result to its tool-call identifier. - Stop only on a final model response, and return its text.…
Reported interview periodApr 2026–Aug 2026
A profiler periodically records the active call stack. Convert these snapshots into the minimal sequence of call-start and call-end events.
Practice focusEach sample has an integer timestamp and a stack ordered from outermost to innermost. Each output event contains the sample timestamp, an event type ( start or end ), and a frame name. Rules - Compare each stack with the previous stack using the longest common prefix. - End removed frames from innermost to outermost. - Start added frames from outermost to innermost. - Adjacent identical stacks produce no events. - Equal names at different depths represent different invocations. - Do not invent end events for calls still active in the last sample.…
Reported interview periodSep 2025–Aug 2026
Implement attention for batched multi-head NumPy arrays on CPU. Inputs are finite arrays with the same floating-point dtype; dimensions are positive.
Practice focusShapes are q: (B, H, Tq, Dk) , k: (B, H, Tk, Dk) , and v: (B, H, Tk, Dv) . Return an array of shape (B, H, Tq, Dv) . When return weights=True , return (output, weights) , with weights of shape (B, H, Tq, Tk) . Requirements - Compute scores as q @ k.transpose(-2, -1) / sqrt(Dk) . - Apply softmax along the key-position dimension. - Support an optional boolean mask broadcastable to the score tensor, where false entries cannot receive probability. - Avoid numerical overflow by using a stable softmax or the framework's stable implementation.…
Reported interview periodOct 2025–Aug 2026
Given a directory of source images and a directory of transformation specifications, produce one output for every image/specification pair. Each specification contains an ordered sequence selected from grayscal…
Practice focusUse the provided naming callback for every result. Apply transformations in order and save valid output images. Scaling truncates the computed dimensions to integers; rotation expands the canvas. Requirements and edge cases - Discover supported image and specification files recursively or according to the supplied listing helper. - Do not share mutable image objects across independent pipelines. - Ensure all scheduled work completes before returning and propagate worker failures.…
Reported interview periodSep 2025–Aug 2026
Walk a directory tree and return groups of files whose complete byte contents are identical.
Practice focusEach returned path must be absolute and resolved. Omit groups containing only one file. Group and path order are not significant. Requirements - Skip symbolic links and continue past files that become unreadable. - Treat multiple empty files as duplicates. - Avoid reading every byte of every file when cheap evidence can rule out equality. - A full-content comparison or collision-resistant digest must confirm every reported group. - Stream large files in bounded-size blocks rather than loading them entirely into memory.…
Reported interview periodOct 2025–Jul 2026
Complete an LRU cache that memoizes arbitrary function calls and survives process restart using an append-only write-ahead log.
Practice focusRequirements - Keys must include function identity and recursively canonicalized arguments. - Keyword insertion order must not affect identity; nested lists and dictionaries must be supported. - Hits return the stored value without executing the function and become most-recently used. - Append a complete record for every access before returning, so replay reconstructs values and recency. - Enforce capacity during both live operation and replay.…
Reported interview periodOct 2025–Jul 2026
Process timestamped commands over records that map string keys to string field/value pairs. Timestamps are unique and strictly increasing; each command returns one string.
Practice focusCommand contract Every command is a list of strings. t , ttl and target are decimal integer strings. Command timestamps t are nonnegative and strictly increasing across the entire input; ttl is positive. Keys and field names are nonempty strings. Values may be empty strings. Inputs contain only the commands below with the stated argument counts. Return one output string for each input command, in order. | Command | Output | | --- | --- | | ["SET", t, key, field, value] | "" ; replace the field with a permanent value.…
Reported interview periodJun 2026–Jul 2026
A small virtual machine executes a list of instructions over one integer accumulator. Blank lines and comment lines are ignored.
Practice focus- plus n : add n to the accumulator and move to the next instruction. - next n : ignore n and move to the next instruction. - jump n : move to the instruction at current index + n . Execution halts when the program counter moves outside the instruction list. It loops when it is about to execute an instruction that has already run. Exactly one jump or next instruction was swapped while keeping its operand. Interface Return -1 from the first two functions if the original program already halts.…
Reported interview periodJan 2025–Jul 2026
Implement an in-memory banking service whose operations arrive in nondecreasing timestamp order.
Practice focusRequirements - Account creation starts at zero and returns True , or False if that identifier is already active. Deposits and withdrawals return the total balance, including held funds; invalid accounts or invalid amounts return None . A zero deposit is a read of the current balance. Negative deposits, and zero or negative withdrawals and transfers, are invalid. - Starting a transfer requires both accounts to exist and available funds (total balance minus holds) to cover the amount.…
Reported interview periodSep 2025–Jun 2026
Given an input string and a vocabulary, tokenize from left to right using longest-prefix matching.
Practice focusAt each position, emit the integer ID of the longest vocabulary entry matching the remaining text. If nothing matches, emit vocab["UNK"] and advance by one character. With collapse unk=True , collapse consecutive unknown IDs into a single ID; otherwise emit one for each unmatched character. The literal vocabulary entry UNK is reserved and must not match input text as an ordinary token. Assume every token has a distinct integer ID and the vocabulary contains UNK . Requirements and edge cases - Return an empty list for empty input.…