#data structure design

20 data structure design interview questions, asked at Google, Netflix, Snowflake and 6 more companies. Last asked Sep 2026.

Insert, delete and get random in O(1) with duplicatesCodingDesign a collection of integers that allows duplicates and supports, each in average O(1) time: 1. insert(val): add one copy of val; return whether val was absent before. 2…
Last asked Sep 2026
Rotating title picker for a home-page billboardCodingBuild a component that picks which title to show next in a billboard (or plays next in a playlist). Every title has a relevance score, and scores can change at any time. Each call…
Last asked Sep 2026
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Snapshot 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
Throne inheritance without an initial kingCodingModel a royal family's line of succession: people are born to parents, people die, and you return the current order of inheritance (a pre-order walk of the family tree that skips…
Last asked Sep 2026
Deduplicate titles across a home page's visible rowsCodingA home page shows rows (shelves) of titles, and only the first few titles of each row are visible on the first screen. The same title may appear in several rows. Choose what to…
Last asked Jul 2026
Priority task executor with duplicate task idsCodingImplement an executor that accepts tasks, each with an id and a priority, and runs them highest priority first. The same task id can be submitted more than once. Decide and…
Last asked Jun 2026
Command executor with undoCodingImplement a class that executes commands and can undo them: execute(command) applies it and records it, and undo() reverts the most recent command that has not been undone. Decide…
Last asked Apr 2026
Concurrent latency percentile trackerCodingBuild a component that records request latencies from many threads and answers percentile queries such as p50, p95 and p99. Discuss exact versus approximate approaches (sorted…
Last asked Feb 2026
Waitlist with top-K and bottom-K queriesCodingBuild a waitlist. People join with a priority (or a join time), can leave, and the system answers two queries at any moment: the top k entries and the bottom k entries. Choose…
Last asked Feb 2026
Min stackCodingDesign a stack that supports push, pop, top and returning the current minimum element, each in constant time. Explain how the minimum stays correct after pops, how you handle…
Last asked Feb 2026
Hit counter over a sliding time windowCodingBuild a counter that records events with timestamps and reports how many happened in the last five minutes. Timestamps arrive in non-decreasing order. Reported variants: counts…
Last asked Jan 2026
Playlist with add, remove and shuffleCodingImplement a video playlist that supports adding a title, removing a title and shuffling the order, along with playing the next title. Aim for constant-time add and remove, a fair…
Last asked Jan 2026
Design a hit counterCodingImplement a counter with hit(timestamp) and gethits(timestamp), where gethits returns the number of hits in the last five minutes. Timestamps arrive in order. Follow-ups: many…
Last asked Jan 2026
Logger that reports its top K messagesCodingBuild a logger that receives messages over time and can return the k most frequent messages at any point. Choose structures so logging stays fast and the top-K query is efficient…
Last asked Jan 2026
Many timers on top of one underlying timerCodingThe system offers a single timer: setting it replaces any earlier setting, and it calls a handler when it expires. Build a class that supports many independent timers on top of…
Last asked Dec 2025
Autocomplete with a trieCodingBuild an autocomplete: insert words (optionally with counts) into a trie, and for a prefix return the matching words, for example the most popular few. Make sure results are…
Last asked Sep 2025
Allocate servers from a pool of mixed node typesCodingA pool holds servers of several node types. Requests ask for a number of servers of a given type; the allocator hands them out and takes them back on release. Design the class and…
Last asked Sep 2025
Implement a trie (prefix tree)CodingImplement a prefix tree over strings: insert a word, check whether a whole word is present, and check whether any stored word starts with a given prefix. Design the classes so…
Last asked Aug 2025
Log manager that evicts the least important logsCodingDesign a log manager that keeps at most totalmax logs. Each log has an importance; when a new log would go over the limit, the least important logs are deleted automatically…
Last asked Aug 2025
Average speed at a point on a road with overlapping reportsCodingA straight road is modeled as the number line from position 0 to 10^9. Vehicles send speed reports. Each report says that traffic on the half-open segment start, end) moved at…