DSA Mastery.beta

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The problem bank

Problems.

Original problems set at Kestrel, each tied to the concept it practises. Python and JavaScript run in your browser; Java and C++ run on the judge.

BFS and DFS on a grid

1Not solved yetRepaint a region of map tilesdfseasy
2Not solved yetCount the rack blocks on a warehouse floordfseasy
3Not solved yetFewest moves to a pickup pointgrid-bfseasy
4Not solved yetMinutes until a config reaches every serverbfseasy

Hash table internals

1Not solved yetThe busiest payment shardhashingeasy
1Not solved yetHow long are the chains?hashingmedium
2Not solved yetGrowing a session tablehashingmedium
2Not solved yetLookup cost in a chained tablehashinghard
3Not solved yetOrder codes that land in the same buckethashingmedium

Seen-set and complement

1Not solved yetFour ledgers that balancehashingmedium
1Not solved yetThe first replayed requesthashingeasy
2Not solved yetThe farthest matching pairhashingmedium
2Not solved yetA refund pair for a totalhashingeasy
3Not solved yetTrack pairs that fill whole slotshashingmedium

Merging sorted sequences

1Not solved yetMerge two devices' message logsmerge-sorted, two-pointerseasy
2Not solved yetDocuments in both posting listsmerge-sorted, two-pointerseasy
3Not solved yetWhen the dock and the driver are both freemerge-sorted, two-pointersmedium

Opposite ends

1Not solved yetMirror reference codesopposite-ends, two-pointerseasy
1Not solved yetTwo parcels for the spare capacityopposite-ends, two-pointerseasy
2Not solved yetGift pairs within the budgetopposite-ends, two-pointers, sortingmedium
2Not solved yetSquared clock drifts in orderopposite-ends, two-pointers, merge-sortedeasy
3Not solved yetFewest cargo bikes for the roundopposite-ends, two-pointers, greedy, sortingmedium

Read and write pointers

1Not solved yetCompact the log bufferread-write-pointers, two-pointerseasy
2Not solved yetTrim repeated postingsread-write-pointers, two-pointersmedium
3Not solved yetCompress repeated scansread-write-pointers, two-pointersmedium

3-sum

1Not solved yetClosest balance snapshots of two accountsmerge-sorted, two-pointers, sortingmedium
1Not solved yetThree products for a gift cardk-sum, two-pointers, sortingmedium
2Not solved yetThree parcels closest to the pallet limitk-sum, two-pointers, sortingmedium
2Not solved yetFour batches that net to zerok-sum, two-pointers, sortinghard
3Not solved yetAd slot triples under the page budgetk-sum, two-pointers, sortingmedium

Three-way partition

1Not solved yetFirst use of each idempotency keyread-write-pointers, two-pointers, hashingeasy
1Not solved yetGroup parcels by priority classthree-way-partition, two-pointerseasy
2Not solved yetBids around the reserve pricethree-way-partition, two-pointersmedium
2Not solved yetTyped queries with backspacesread-write-pointers, two-pointersmedium
3Not solved yetThe k-th fastest pickupthree-way-partition, two-pointers, top-kmedium

At most K and exactly K

1Not solved yetFee stretches within the allowancesliding-window-variable, at-most-kmedium
1Not solved yetLongest segment covering at most two zonesat-most-k, sliding-window-variable, hashingmedium
2Not solved yetStretches with exactly k clicksat-most-k, prefix-sum-hashmap, sliding-window-variablemedium
2Not solved yetLongest healthy stretch with k re-runsat-most-k, sliding-window-variablemedium
3Not solved yetSessions with exactly k categoriesat-most-k, sliding-window-variable, hashinghard

Sliding window: fixed and variable windows

1Not solved yetBusiest stretch on the launch dashboardsliding-window-fixedeasy
1Not solved yetRepeated order inside k arrivalssliding-window-fixed, hashingeasy
2Not solved yetError bursts on the status pagesliding-window-fixedeasy
2Not solved yetFirst slow stretch in a surge zonesliding-window-fixedmedium
3Not solved yetLongest delivery run in one shiftsliding-window-variablemedium
4Not solved yetLongest fresh listening sessionsliding-window-variable, hashingmedium
5Not solved yetFewest hours to a revenue targetsliding-window-variablemedium

Minimum covering window

1Not solved yetFewest parcels from both endssliding-window-variable, window-countshard
1Not solved yetShortest log window with every required codeminimum-cover, sliding-window-variable, hashingmedium
2Not solved yetShortest block to rebalance the build queueminimum-cover, sliding-window-variable, hashinghard
2Not solved yetShortest stretch where every member postsminimum-cover, sliding-window-variable, hashingmedium
3Not solved yetShortest browsing span with every wishlist itemminimum-cover, sliding-window-variable, hashinghard

Windows with counts

1Not solved yetDistinct tracks in every k-play windowwindow-counts, sliding-window-fixed, hashingeasy
1Not solved yetScrambled blocked terms in a descriptionwindow-counts, hashing, sliding-window-fixedmedium
2Not solved yetWindows dominated by one topicwindow-counts, hashing, sliding-window-fixedmedium
2Not solved yetReordered batch in a scan streamwindow-counts, sliding-window-fixed, hashingmedium
3Not solved yetBest bundle of distinct productswindow-counts, sliding-window-fixed, hashingmedium

Linked lists

1Not solved yetNewest first in a chat threadlinked-listseasy
2Not solved yetThe middle of a reply chaintwo-pointers, linked-listseasy
3Not solved yetMerge two shards' log chainsmerge-sorted, linked-listseasy
4Not solved yetUnsend the k-th newest messagetwo-pointers, linked-listseasy