Persistent key-value store with binary snapshotsCodingImplement an in-memory key-value store whose whole state can be saved to, and restored from, a storage medium that holds a single binary blob. You are given: Implement
Last asked Oct 2026
#hash map
+5Implement an LRU cacheCodingImplement a least-recently-used cache with get(key) and put(key, value), both in O(1) time, with a fixed capacity.Last asked Oct 2026
+3In-memory file system with files and foldersCodingImplement an in-memory file system with path-based file and folder access, plus follow-ups on per-directory limits, duplicate names and identical contents. Covers the bank's vault…Last asked Oct 2026
Match payments to invoices by memo and amountCodingA billing system has to match incoming payments to open invoices. Both arrive as comma-separated strings. - Invoice: invoiceid,amount,duedate. The amount is an integer in cents…Last asked Sep 2026- Monthly AI token billing with plan switchingCodingYou are building the monthly invoice step for a chat-based AI product that charges by token usage. Each chat session produces one record, given as a comma-separated string with…Last asked Sep 2026
+1Task manager with user quotas and expiring assignmentsCodingBuild an in-memory TaskManager in four levels. Each level adds methods to the same class, and you move to the next level only after the current one passes. Every method takes an…Last asked Sep 2026
Weighted cache that evicts the heaviest entriesCodingImplement WeightedCache, a key-value cache with a total-weight budget instead of an item count. Each entry has a positive integer weight. After every put, the sum of the weights…Last asked Sep 2026- +2Banking system with transfers, cashback and account mergesCodingBuild an in-memory banking system in four levels. Each level adds methods, and every earlier method must keep working. Every call takes a timestamp in milliseconds as its first…Last asked Sep 2026
- +1Social follow graph with point-in-time snapshotsCodingBuild an in-memory follow graph that can answer questions about its own past. Follows are directed: a following b says nothing about b following a. Implement a SocialNetwork…Last asked Sep 2026
+2Crash-safe on-disk key-value storeCodingBuild a filesystem-backed hash table that survives crashes and restores every entry from the latest state on restart. Reported on 1point3acres' Baseten bank; reconstructed in our…Last asked Sep 2026
+7LRU cacheCodingBuild a key-value cache with a fixed capacity that evicts the least recently used entry when it is full. get(key) returns the value or a miss, put(key, value) inserts or updates…Last asked Sep 2026
Key-value store that reports its recent request rateCodingBuild an in-memory key-value store with put and get (delete optional). It must also report how many puts and gets per second it served over a recent stretch of time, say five…Last asked Sep 2026- +2Snapshot set with frozen insertion-order iteratorsCodingImplement SnapshotSet, a set of integers whose iterators are frozen at the moment they are created. - add(value) - bool: insert value. Return False and do nothing if it is already…Last asked Sep 2026
- First position of any anagram of a pattern in a stringCodingReturn the smallest index at which some rearrangement of a query string appears as a contiguous substring of a text, or -1. Keep a running character count over a fixed-size window…Last asked Sep 2026
- +2Rate-limited event loggerCodingBuild a logger that rate-limits repeated events in a stream. Each event has a string name and an integer timestamp in seconds. Timestamps arrive in non-decreasing order, and…Last asked Sep 2026
- +2Cloud storage with user quotas and backupsCodingDesign an in-memory cloud storage service. The interview has four parts. Each part adds methods, and every earlier method must keep working. Implement a class CloudStorage. File…Last asked Sep 2026
+1Oldest one-time visitor in a login streamCodingAn online store wants to know which customers have visited only once. Every login is reported to your service as a username, in the order the logins happen. Implement a class…Last asked Aug 2026- Reconcile bank account balances across two datasetsCoding1. From a list of balance records for bank accounts, return the latest balance of an account, in the output format the tests expect. 2. A second dataset is added. Reconcile the…Last asked Aug 2026
Parse URL query parameters with repeated and nested keysCodingA web service receives HTTP GET requests. The part of the URL after the first ? is the query string. Write a parser that turns it into a dictionary. Implement parsequery(url: str)…Last asked Aug 2026
Select table cells and set a colorCodingDesign a Table class for a whiteboard app. A table has a fixed number of rows and columns. A user selects part of the table and sets a color on everything selected. Every cell…Last asked Aug 2026- Highway toll checkpoints from plate logsCodingA highway has numbered toll checkpoints. Each checkpoint's name contains its position as a number, for example "A1" is at position 1 and "CP12" is at position 12. Ignore every…Last asked Aug 2026
- +1Recipe manager with ingredient searchCodingBuild an in-memory recipe book. Each recipe has a name, an ordered list of ingredients and an ordered list of steps. The work comes in two parts; finish part 1 before you start…Last asked Jul 2026
- +1Design layer document with undo, redo and batchesCodingYou are building the core of a design tool. A document holds layers. Each layer has a unique integer id and a set of string properties, such as color, shape or size. A layer does…Last asked Jul 2026
- +1Copy a linked list with random pointersCodingEach node of a linked list has a next pointer and a random pointer that can point at any node or nowhere. Make a deep copy of the list. Do it with a map from old nodes to new…Last asked Jun 2026
Top K error strings in a time windowCodingGiven request-response log entries with timestamps, report the K most frequent errors inside a sliding time window. Reported on 1point3acres' Notion bank; reconstructed in our own…Last asked Jun 2026
+1Reconstruct a string from chained segmentsCodingA log-shipping service splits a long message into fragments and sends them out of order. Each fragment is a triple startid, endid, payload: it covers the stretch from marker…Last asked May 2026- +3In-memory SQL table with filtering and multi-key sortingCodingBuild a small in-memory SQL-like database. You do not need to parse SQL text. Queries arrive as structured arguments. Implement SQLManager: - createtable(name: str, columns:…Last asked May 2026
- +1Fill placeholders in a template stringCodingWrite a function that fills in a template string. template may contain placeholders written as {name}. The text between the braces is a variable name. keysi is a variable name and…Last asked May 2026
+3Key-value store with nested transaction rollbackCodingImplement an in-memory key-value store whose string keys map to string values. It supports transactions, and transactions can be nested. Implement the class KeyValueStore: -…Last asked May 2026- Multiply two sparse matricesCodingMultiply two matrices that are mostly zeros. Skip the zero entries: store only the non-zero values of each matrix (by row or as lists of positions) and multiply only those pairs…Last asked May 2026
- Account balances from a transaction logCodingA payments system receives a log of transactions and must turn it into account statements. Each log entry is a string with four comma-separated fields: - transactionid: a unique…Last asked May 2026
+1Live top-k best-selling books leaderboardCodingA bookstore wants a live leaderboard of its best-selling books. Sales arrive one at a time, and the leaderboard can be read at any moment. Implement a BookSalesTracker class: -…Last asked May 2026
Key-value store with constant-time set-allCodingImplement a key-value store with set, get and a setAll operation that assigns one value to every key, all in O(1). A related variant manages dataset sizes under a fixed disk…Last asked Apr 2026- Inner join of two CSV datasetsCodingTwo systems export CSV data that you need to combine. Implement: Each dataset is a list of lines. The first line is a header of comma-separated column names. Every other line is a…Last asked Apr 2026
- +2Shortest subarray with at least k distinct valuesCodingYou are given an integer array arr and an integer k. Call a contiguous subarray good if it contains at least k different values. Return the length of the shortest good subarray…Last asked Apr 2026
- Per-user token bucket limiter with interval refillsCodingBuild a per-user token rate limiter for an AI API. Every user has their own policy, and one user's traffic never affects another's. A policy has three positive integers: -…Last asked Apr 2026
- Settle group debts with the fewest transfersCodingA group of people owe each other money, given as transfers (from, to, amount). Return the smallest number of transfers that brings every person's balance to zero.Last asked Feb 2026
- Count subarrays that sum to KCodingGiven an array of integers (negatives allowed) and k, count the contiguous subarrays whose sum is exactly k. Keep running prefix sums and a map from each prefix sum to how often…Last asked Feb 2026
- Total listener time per live audio room from an event logCodingA time-ordered log records rooms being created and users joining and leaving them. Compute the total user-time spent in each room, handling users who never leave and rooms that…Last asked Feb 2026
Compress a vertex list into unique vertices and indicesCodingTurn a list of vertex tuples into a list of unique vertices in first-seen order plus an index array that rebuilds the original list.Last asked Feb 2026- +1LRU cache with runtime resizingCodingImplement a least recently used (LRU) cache whose capacity can change while it is in use. - get(key) returns the value for key, or -1 if it is not cached. A successful get makes…Last asked Feb 2026
- Shipping cost with tiered pricingCodingAn order names a country and the products and quantities in it, and a pricing table gives the shipping cost of each product for each country. 1. Compute the order's total shipping…Last asked Jan 2026
- Card authorization report with fraud rulesCodingA payment platform receives authorization requests: a card holder's intent to pay a merchant. Write a function that decides each request and returns a report. Each request is a…Last asked Jan 2026
- Resolve user roles across an account hierarchyCodingAccounts form a hierarchy, and users are given roles on accounts. Given the hierarchy and the role assignments, work out the roles a user has on a given account, including roles…Last asked Jan 2026
- Link similar user records by weighted field matchesCodingA data-quality team wants to find user profiles that probably belong to the same person. You get records, a 2D list of strings. The first row is a header of field names, and one…Last asked Jan 2026
Party hours and quiet gaps by neighborhood and cityCodingA community events app records every party in two separate lists that share a partyId: - partyWindows: rows of partyId, start, end. start and end are hours as strings, and a party…Last asked Dec 2025- Report timed-out simulations from start, ping and end eventsCodingSimulations send start, ping and end events with timestamps. After each new event, return the simulations whose last activity is now older than the timeout and that have not ended.Last asked Dec 2025
- Most frequent key without max()CodingGiven a list of keys, return the one that appears most often without using the built-in max(). Count with a dictionary, track the best as you go, and decide how ties are broken.Last asked Nov 2025
- Fleet capacity after server id replacementsCodingA service runs on a fleet of n servers. Each server has an integer id, and a server with id x can handle x requests at a time. The fleet's total capacity is the sum of all server…Last asked Sep 2025
Cache with expiry, priority and LRU evictionCodingImplement a fixed-capacity key-value cache, PriorityExpiryLRUCache. Every item stores a value, an integer priority, and an expiry time. When a new key arrives and the cache is…Last asked Aug 2025- Top three scores for each studentCodingGiven records of student ID and score, return each student's three highest scores. Group by student and keep the top three with a small heap; when you learn that scores are whole…Last asked Aug 2025
- Palindrome pairsCodingGiven a list of distinct words, return every pair of indices (i, j) where wordsi + wordsj is a palindrome. Checking all pairs is too slow; put the reversed words in a hash map (or…Last asked Aug 2025
- Rank vehicles by peer-to-peer update contributionCodingA fleet of electric vehicles receives over-the-air software updates split into fixed-size chunks. Chunks come from the distribution server over cellular data, which is expensive…Last asked Jul 2025
- Group prompts into templates under concurrent ingestionCodingAn API receives prompts from many threads. Most come from a few templates filled with different values: Summarize ticket 48213 for alice@acme.com and Summarize ticket 1007 for…
Match words against a letter patternCodingGiven a pattern string and a list of words, decide for each word whether it follows the pattern. A word follows the pattern when it has the same length as the pattern and the…- +1Recent search history with a size limitCodingBuild the recent-searches list behind a search box. When the user focuses the box, it shows their most recent distinct searches, newest first. Every search the user runs is…
Count recipes a pantry can coverCodingYou keep a pantry of ingredients, written as a string pantry. Each character is one unit of an ingredient, so "aab" holds two units of a and one unit of b. You also have a list of…
Folder path from a node idCodingA file browser stores its folder hierarchy as three parallel arrays: - idListi is a unique folder id. - childreni lists the ids of the folders directly inside folder idListi. -…- One-hot encode an integer arrayCodingWrite onehot(arr: listint) - listlistint that returns the one-hot encoding of an integer array as a 2D list. - The matrix has one row per element of arr, in the same order. - It…
- +1Root of the largest tree in a forestCodingYou are given a list relations. Each entry child, parent says that parent is the direct parent of child. Together the relations form a forest: there are no cycles, and every node…
- Key-value store with prefix searchCodingBuild an in-memory key-value store whose values can also be looked up by key prefix. Keys are strings and values are integers. Implement the KVStore class: - KVStore() creates an…
- +1Group duplicate records that share any propertyCodingYou are given a list of records. Each record has a unique integer ID and three properties, for example a name, an email and a phone number: Two records are duplicates when they…
- Count redundant substrings by vowel and consonant weightsCodingWrite a function that counts the redundant substrings of a word. A string s is redundant when its length equals a V + b C, where V is the number of vowels in s, C is the number of…
- Frequent user events within a 24-hour windowCodingYou are given a list of activity log entries. Each entry has a userid (string), a timestamp (integer seconds since epoch) and an eventtype (string). The list is not sorted…
- Recent file tracker with date and insertion orderCodingImplement a FileStorageSystem class that records files and answers two kinds of listing queries. - storefile(file: str, date: str) - None records a file with its storage date…
- Sort words by a custom alphabetCodingYou are given a string order that lists characters from first to last in a custom alphabet. Each character appears in order at most once. You are also given a list of strings…
- +2Count distinct values in every sliding windowCodingGiven an integer array nums and a window size k, return a list with one entry per contiguous window of length k (there are len(nums) - k + 1 of them). Each entry is the number of…
- Server load scores from a day of requestsCodingA load balancer team wants a daily stress report for its server fleet. You get three inputs for one day: - servers: lines serverid,basescore. Every server starts at its integer…
- Cloud usage bill from regional hourly ratesCodingYou are writing the billing step for a cloud platform. A customer's usage report says which region they ran in and how many hours they used each service. A pricing table gives the…
- Build the longest spike from an arrayCodingA spike is a sequence of integers that strictly increases up to a single peak and then strictly decreases. The peak belongs to both parts, and either part may be empty, so a…
- +1Longest palindrome from equal-length wordsCodingYou are given a list of words. Every word has the same length k and uses lowercase letters. The list can contain duplicates. Pick some of the words (possibly none) and join them…
- Per-domain sliding-window rate limiterCodingA gateway receives requests one at a time, at most one per second. Each request names a domain. Build a rate limiter that keeps its state between calls and decides, for each…
- Match applicant skills and versions to a job's requirementsCodingAn applicant tracking system screens candidates by the skills they list. Each applicant gives one comma-separated string of skills, strongest first. A job posting gives a…
- Poker hand checker with jokersCodingWrite isvalidhand(hand: liststr) - bool for a five-card poker game. Each card is a string "<rank of <suit". The rank is 2 to 10, J, Q, K or A. The suit is hearts, diamonds, clubs…
Apply ordered token merges to a stringCodingMany language models read text as a list of token ids. In this scheme, every token after the single characters is built from two earlier tokens, and turning text into ids means…- In-memory note-taking system with keyword searchCodingDesign an in-memory note-taking system, SecondBrainSystem. Each note gets a unique id and carries metadata about when it was created and last modified. Callers pass the current…
- Count stable server segmentsCodingA row of n machines has integer capacities capacity0..n-1. A contiguous segment l, r is stable when all of these hold: 1. It contains at least 3 machines (r - l = 2). 2. The two…