Product-minded loops with practical coding rounds — string and array manipulation with fiddly edge cases shows up often, and design rounds stay grounded in surfaces like feeds and boards.
Typical loop
- 1Recruiter screen
- 2Technical phone screen: one coding problem
- 3Onsite: two coding rounds
- 4System design round
- 5Behavioral / cross-functional round
Questions
Callback's practice questions and the LeetCode questions Pinterest has been asking, filtered together.
Practice questions
Algorithms & Data Structures · Greedy line packing and fiddly space math — full text justification.
System Design · Token bucket, sliding window, and where the counters live.
Algorithms & Data Structures · Arbitrary-precision rounding — floats need not apply.
Algorithms & Data Structures · Streaming design: recent counts, top-k, and sliding-window bans.
Algorithms & Data Structures · Order and duplicates vanish at every depth — canonicalize.
Assign Pins to Shortest Columns
Algorithms & Data Structures · The masonry-layout greedy: shortest column wins, leftmost on ties.
Collect Pins from Reachable Boards
Algorithms & Data Structures · BFS over the bipartite pin-board graph without building board-to-board edges.
Algorithms & Data Structures · Reassemble lines from arbitrary chunks, reading lazily.
Algorithms & Data Structures · Advance players in O(1), rank them without sorting — a linked list per room.
Algorithms & Data Structures · Meet new group sizes while disrupting as few buckets as possible.
Algorithms & Data Structures · Interval sweep for the free ranges — independent of bucket-space size.
Algorithms & Data Structures · Smallest-free allocation under a capacity that moves at runtime.
Cross-Reference Logs to Flag Spam Numbers
Algorithms & Data Structures · A hash join across two logs — and saying that word out loud.
Sparse Matrix Storage, Addition, and Multiplication
Algorithms & Data Structures · Storage proportional to nonzeros — and the cancellation trap.
Select the Nearest Eligible Elevator
Algorithms & Data Structures · A requirements-gathering problem wearing a simulation costume.
Decide Target via Subsequence Plus/Multiply Expression
Algorithms & Data Structures · Expression search with precedence — the (total, pending product) trick.
Compute Reachable Cells for a Cleaning Robot
Algorithms & Data Structures · Slide-until-blocked physics: rest positions are the states, not cells.
Maximize Boxes Stored Through One Entrance
Algorithms & Data Structures · Prefix-min ceilings plus an exchange-argument greedy.
Mark and Compact a Heap-Indexed Subtree
Algorithms & Data Structures · Garbage collection in miniature: mark a subtree, compact, remap.
Algorithms & Data Structures · Pack named ID ranges, then resize with all-or-nothing shifts.
Algorithms & Data Structures · Net the balances, then match debtors to creditors greedily.
Algorithms & Data Structures · Use every ticket once: Hierholzer's walk, smallest destination first.
Algorithms & Data Structures · Two sorted indexes and a binary search you write by hand.
Algorithms & Data Structures · BFS over routes, not stops — clear each stop as you expand it.
Algorithms & Data Structures · Two out-edges per index: a graph search with a visited array.
Restaurant Seating: Free Intervals
Algorithms & Data Structures · A +ppl/−ppl sweep; occupancy is constant between events.
Count Pins on a Two-Column Screen
Algorithms & Data Structures · Only n scroll offsets matter — slide the window to a pin's top.
Count Subarrays with Score Below K
Algorithms & Data Structures · Positives make sum × length monotone — a two-pointer window.
Count Objects in a Pixel Grid via an API
Algorithms & Data Structures · Flood fill through an opaque API — isSameObject is the catch.
Algorithms & Data Structures · Open roads cost 0, closed cost 1 — textbook 0-1 BFS.
Algorithms & Data Structures · A min-heap of (free time, agent) — tuple order breaks the ties.
Algorithms & Data Structures · lower_bound on the prefix itself, then one startswith check.
Stateful Search Autocomplete Session
Algorithms & Data Structures · A typing session over search counts: top three by frequency, then alphabetically.
Algorithms & Data Structures · Parse (count, digit) pairs backward — adjacent runs must differ.
System Design · Recsys serving, not a social timeline — retrieval funnels, session state, four nines.
System Design · Fan-out, viral-pin aggregation under skew, and deciding not to send.
System Design · Tries with precomputed top-k, prefix sharding, and freshness by atomic swap.
Design an Ads Event Reporting System
System Design · Streaming for dashboards, batch for billing truth — and hot keys from viral ads.
Design a Merchant Catalog Update Pipeline
System Design · Idempotent bulk ingestion with per-item ordering, fairness, and safe deletions.
Design Image Upload and Serving for Pins
System Design · Presigned uploads, content-addressed variants, and a CDN that caches forever.
Design the Pins and Boards Data Model
System Design · Sharding a relational model: object tables, mapping tables, no cross-shard joins.
System Design · Embeddings, sharded ANN retrieval, and fresh pins searchable in seconds.
System Design · Metadata plane vs data plane, chunk replication, and the atomic-commit moment.
Algorithms & Data Structures · Split the nonzero balances into as many zero-sum groups as possible.
Algorithms & Data Structures · Rebuild the itinerary with Hierholzer's walk, then look for a repeat.
Algorithms & Data Structures · BFS from the start: the layer where the last index appears is the answer.
Algorithms & Data Structures · The count served by time T is monotone — binary search T.
Algorithms & Data Structures · Matches are contiguous: lower_bound the prefix, then the prefix bumped by one.
Algorithms & Data Structures · The reverse parse, memoized on (index, previous digit) — count, don't build.
Algorithms & Data Structures · Split, round each value with string arithmetic, join — floats need not apply.
Algorithms & Data Structures · Reassemble the lines, net the balances, then search for the fewest transfers.
Asked on LeetCode
45 questions · all time
- Reconstruct ItineraryhardArrayStringDepth-First SearchGraph Theory+5frequency 100.0
- Optimal Account BalancinghardArrayDynamic ProgrammingBacktrackingBit Manipulation+1frequency 96.5
- Bus RouteshardArrayHash TableBreadth-First Searchfrequency 94.1
- Expression Add OperatorshardMathStringBacktrackingfrequency 90.2
- Shortest Way to Form StringmediumTwo PointersStringBinary SearchGreedyfrequency 81.7
- Shortest Path in a Grid with Obstacles EliminationhardArrayBreadth-First SearchMatrixfrequency 79.0
- Coin ChangemediumArrayDynamic ProgrammingBreadth-First SearchKnapsack Problem+1frequency 77.0
- Count Subarrays With Score Less Than KhardArrayBinary SearchSliding WindowPrefix Sumfrequency 77.0
- Count and SaymediumStringfrequency 69.2
- Design Search Autocomplete SystemhardStringDepth-First SearchDesignTrie+3frequency 69.2
- Is SubsequenceeasyTwo PointersStringDynamic Programmingfrequency 67.6
- Maximum Profit in Job SchedulinghardArrayBinary SearchDynamic ProgrammingSortingfrequency 67.6
- Split Array Largest SumhardArrayBinary SearchDynamic ProgrammingGreedy+1frequency 67.6
- Find Median from Data StreamhardTwo PointersDesignSortingHeap (Priority Queue)+1frequency 65.8
- Longest Word in DictionarymediumArrayHash TableStringTrie+1frequency 63.8
- Target SummediumArrayDynamic ProgrammingBacktrackingKnapsack Problem+1frequency 63.8
- Find Median Given Frequency of NumbershardDatabasefrequency 61.5
- Meeting Rooms IIIhardArrayHash TableSortingHeap (Priority Queue)+1frequency 61.5
- Delete Nodes And Return ForestmediumArrayHash TableTreeDepth-First Search+1frequency 59.0
- Design A LeaderboardmediumHash TableDesignSortingfrequency 56.0
- Put Boxes Into the Warehouse ImediumArrayGreedySortingfrequency 56.0
- Put Boxes Into the Warehouse IImediumArrayGreedySortingfrequency 56.0
- Sparse Matrix MultiplicationmediumArrayHash TableMatrixLinear Algebrafrequency 56.0
- Find Minimum Time to Finish All JobshardArrayDynamic ProgrammingBacktrackingBit Manipulation+1frequency 52.5
- Multiply StringsmediumMathStringSimulationfrequency 52.5
- Reorganize StringmediumHash TableStringGreedySorting+2frequency 48.3
- Accounts MergemediumArrayHash TableStringDepth-First Search+3frequency 42.8
- Candy CrushmediumArrayTwo PointersMatrixSimulationfrequency 42.8
- Combination SummediumArrayBacktrackingfrequency 42.8
- Dot Product of Two Sparse VectorsmediumArrayHash TableTwo PointersDesign+1frequency 42.8
- Letter Combinations of a Phone NumbermediumHash TableStringBacktrackingfrequency 42.8
- String CompressionmediumTwo PointersStringfrequency 42.8
- Text JustificationhardArrayStringSimulationfrequency 42.8
- Add Two Numbers IImediumLinked ListMathStackfrequency 35.2
- Corporate Flight BookingsmediumArrayPrefix Sumfrequency 35.2
- Employee Free TimehardArraySweep LineSortingHeap (Priority Queue)frequency 35.2
- Find First and Last Position of Element in Sorted ArraymediumArrayBinary Searchfrequency 35.2
- Meeting Rooms IImediumArrayTwo PointersGreedySorting+2frequency 35.2
- Merge IntervalsmediumArraySortingQuicksortfrequency 35.2
- Merge k Sorted ListshardLinked ListDivide and ConquerHeap (Priority Queue)Merge Sort+1frequency 35.2
- Number of IslandsmediumArrayDepth-First SearchBreadth-First SearchUnion-Find+1frequency 35.2
- Number of ProvincesmediumDepth-First SearchBreadth-First SearchUnion-FindGraph Theoryfrequency 35.2
- Rotting OrangesmediumArrayBreadth-First SearchMatrixfrequency 35.2
- The MazemediumArrayDepth-First SearchBreadth-First SearchMatrixfrequency 35.2
- Top K Frequent ElementsmediumArrayHash TableDivide and ConquerSorting+4frequency 35.2