xAI interview questions for engineers

Topic tags
Python

Reported interview periodNot available

Fixed-Window Token Limiter

Implement a per-key limiter with one shared token limit and fixed window length. Commands are:

Practice focus- ("ALLOW", key, cost, timestamp) : accept if the key's usage plus cost does not exceed the limit; a rejected request consumes nothing. - ("RESET", key, timestamp) : clear that key's usage in the fixed window containing timestamp . The window containing time t starts at (t // window) window . Costs are non-negative integers; zero is allowed. Preserve input order. Return one result per command, using booleans for ALLOW and a consistent acknowledgment for RESET .…

New public brief

Topic tags
Python
Concurrency

xAICoding

Talk-through codingNo local grader

Reported interview periodNov 2025–Apr 2026

Make a Bank Account Thread-Safe

You are given a BankAccount whose deposit method performs a read-modify-write operation and may pause between reading and writing. You cannot modify that class. Implement a subclass that makes deposits safe whe…

Practice focusCall the inherited implementation rather than copying it. Two deposits of 500 and 700 into an account starting at 0 must finish with 1200 . Ensure the lock is released if the inherited method raises. The supplied constructor creates the account and its lock. Complete deposit only. The provided run case adapter owns the concurrent fixture execution; it is not candidate work. Opening balances and deposit amounts are integers, and deposit amounts are nonnegative. Empty deposit lists leave the opening balance unchanged. Each successful call returns None .…

New public brief

Topic tags
Python
Data structures
Communication

xAICoding

Python codingWebAssembly + public tests

Reported interview periodApr 2026

Resumable Iterators

Implement an iterator over a copied list that can serialize its position and later resume at the next not-yet-yielded item. Then compose the same behavior across a sequence of lists.

Practice focusSaved state points to the next item, never the last item returned. A completed iterator restores completed. State must be serializable and restoration must not repeat or skip values. The chain state records both the current group and the position within it. Use exactly {"index": integer} for list state and {"outer": integer, "inner": {"index": integer}} for chain state. Reject malformed keys, booleans/nonintegers and negative or out-of-range active indices with ValueError .…

New public brief

Topic tags
Python
Storage & state

xAICoding

Python codingWebAssembly + public tests

Reported interview periodDec 2025–Apr 2026

In-Memory Database with Expiry and Snapshots

Build an in-memory database in four stages. Each key owns string field/value pairs.

Practice focusMissing values return "" . Scans emit field(value) entries sorted by field. A TTL value is live over [created at, created at + ttl) . A backup captures all live fields and each field's remaining lifetime. Restore selects the newest backup at or before timestamp to restore , replaces current state, and restarts remaining lifetimes at timestamp . Assume timestamps supplied to mutating timed operations are nondecreasing. Backups must not share mutable state with the live database.…

New public brief

Topic tags
Python
Data structures
Storage & state
Networking

xAICoding

Python codingWebAssembly + public tests

Reported interview periodApr 2026

Token-Bucket State Transitions

Each subject has a token bucket stored in a shared key-value cache. A missing bucket begins full. Refill lazily when a request arrives: add elapsed_time * refill_rate, capped at capacity. If time has not advanc…

Practice focusAccept only when the refilled balance covers the full request, then subtract it. A rejected request spends nothing. Persist the refilled state in either case. A backward-moving clock must not create tokens. TokenBucket and the in-memory DistributedCache test double are provided. This base task is sequential; the cache name does not imply atomic distributed behavior. Refill returns a new bucket without editing its argument. Existing buckets retain their stored capacity/refill rate; call configuration initializes missing buckets only.…

New public brief

Topic tags
Python

xAICoding

Python codingWebAssembly + public tests

Reported interview periodFeb 2026

Flatten and Rebuild Nested Values

A nested value contains integer leaves and internal list, tuple, or dict nodes. Dictionaries are traversed in insertion order.

Practice focusImplement: flatten returns leaves in traversal order. unflatten uses structure as a shape template and rebuilds the same container types while replacing leaves from left to right. Raise ValueError when there are too few or too many replacement values, and TypeError for unsupported nodes, including booleans. Empty containers must round-trip. Replacement values must be a list of non-boolean integers; reject other values with TypeError . Do not modify either input.…

Public brief

Topic tags
Python
Data structures

xAICoding

Python codingWebAssembly + public tests

Reported interview periodFeb 2026

Weighted LRU Cache

Build an LRU cache whose capacity is the total weight of stored entries rather than the number of keys.

Practice focusget returns -1 when absent and marks a hit most-recently used. put inserts or replaces a key. On replacement, remove the old weight before checking capacity. Evict least-recently used entries until the new value fits; one insertion may evict several entries. A non-positive size or a size exceeding capacity raises ValueError without changing the cache. Exact fits are valid. Target average O(1) time for get and for each individual insert, update, or eviction. The provided run case owns fixture dispatch and is not candidate work.…

Public brief

Topic tags
Python
Concurrency

xAICoding

Talk-through codingNo local grader

Reported interview periodDec 2025–Jan 2026

Sort Integers with Multiple Workers

Implement an ascending integer sort that divides sufficiently large inputs into chunks, sorts chunks concurrently, and merges the sorted runs.

Practice focusReturn a new list and do not mutate the input. For fewer than 1000 values or a single worker, a direct sort is acceptable. On the large-input path, actually partition the input and dispatch chunk sorts; do not sort the entire list in one call. Cap the worker count to useful work and merge all runs correctly, including duplicates and negative values. The worker count must be a positive integer (not a boolean); reject invalid counts with ValueError before dispatch. Use native worker execution for the concurrent path.…

Public brief

Topic tags
Python
Reliability

xAICoding

Python codingWebAssembly + public tests

Reported interview periodDec 2025

Identify Faulty Nodes with Group Tests

There are n compute nodes with IDs 0 through n - 1. A supplied function test(group) returns True exactly when every node in group is healthy. A test group must contain at least two node IDs. Assume at least two…

Practice focusImplement: Return every faulty node ID in ascending order. Minimize unnecessary tests, but prioritize correctness. Do not assume that testing one node is legal. The supplied run case owns fault labels and the test callback; implement only find faulty nodes . Each test must contain at least two distinct valid non-boolean integer IDs. The public safety budget is at most n (n-1)//2 + n-1 callback calls; it admits pair discovery followed by classification and is not an optimality claim. Nodes are fixed during a run, and n is an integer at least two.…

Public brief

Topic tags
Python
Algorithms
ML / AI
Product design

Coding exerciseCodingAI-generated

Runnable coding45–70 min

Reported interview periodN/A

Build a token-budget batcher

Implement a small batching primitive, then adapt it to padded cost, bounded output, and production reasoning.

Practice focusPython, Greedy algorithms, Boundary cases, ML batching, Complexity through a runnable coding exercise.

Public brief

Topic tags
Python
Algorithms
Data structures
Storage & state
Networking

Coding exerciseCodingAI-generated

Runnable coding45 min

Reported interview periodN/A

Sliding-window rate limiter

Build a limiter, then add quota reporting, retry timing, and independent keys.

Practice focusPython, Queues, State, Boundary cases, Complexity through a runnable coding exercise.

Public brief

Topic tags
Python
Algorithms
Data structures
Product design
Communication

Coding exerciseCodingAI-generated

Runnable coding45 min

Reported interview periodN/A

Interval calendar

Reason about half-open intervals through conflicts, room counts, merging, and free slots.

Practice focusPython, Sorting, Intervals, Heaps, Edge cases through a runnable coding exercise.

Public brief

Topic tags
Python

Coding exerciseCodingAI-generated

Runnable coding45 min

Reported interview periodN/A

Nested dictionary transforms

Flatten and reconstruct nested data, then support path access and lists.

Practice focusPython, Recursion, Data transformation, JSON-like data through a runnable coding exercise.

Public brief

Topic tags
Python
Storage & state

Coding exerciseCodingAI-generated

Runnable coding45 min

Reported interview periodN/A

Command-log store

Evolve a tiny state machine through undo, compaction, and snapshot replay.

Practice focusPython, State machines, Undo logs, Compaction, Persistence through a runnable coding exercise.

Public brief

Topic tags
Python
Data structures
Storage & state

Coding exerciseCodingAI-generated

Runnable coding50 min

Reported interview periodN/A

Streaming metric window

Compute ordered rolling metrics, then partition state and expose freshness explicitly.

Practice focusPython, Queues, Streaming state, Boundaries, Observability through a runnable coding exercise.

Public brief

Topic tags
Python
Data structures

Coding exerciseCoding

Written response35 minutes

Reported interview periodN/A

Grade book

An in-memory grade book with a ranking that does not treat a missing score as zero.

Practice focusState, Ranking, Edge cases through a written response exercise.

Public brief

Topic tags
Python
Algorithms

Coding exerciseCoding

Written response35 minutes

Reported interview periodN/A

Vial log

Return the vials that stayed inside a temperature range for their whole stay.

Practice focusScanning, Missing data through a written response exercise.

Public brief

Topic tags
Python
Algorithms

Coding exerciseCoding

Written response35 minutes

Reported interview periodN/A

Comment batches

Collapse consecutive comments on the same path into one batch.

Practice focusOrder, Grouping through a written response exercise.

Public brief

Topic tags
Python
Algorithms
Data structures

Coding exerciseCoding

Written response40 minutes

Reported interview periodN/A

Launch order

Return one valid order of steps, or report a cycle.

Practice focusOrdering, Cycles through a written response exercise.

Public brief

Topic tags
Python

Coding exerciseCoding

Written responseA weekend

Reported interview periodN/A

Notes table

Turn a folder of notes into a table of titles and word counts.

Practice focusA small program, What you left out through a written response exercise.