Problems

58 of 200 solved

58 solved| 15 in progress

ProblemPathDifficultyStatusConceptTime

Two SumArrays & StringsEasycompletedHash Map Lookup10m Best Time to Buy and Sell StockArrays & StringsEasycompletedKadane's Variant10m Contains DuplicateArrays & StringsEasycompletedSet Usage5m Valid AnagramArrays & StringsEasycompletedFrequency Count8m Product of Array Except SelfArrays & StringsMediumcompletedPrefix/Suffix15m Maximum SubarrayArrays & StringsMediumcompletedKadane's Algorithm12m Container With Most WaterArrays & StringsMediumcompletedTwo Pointers15m 3SumArrays & StringsMediumcompletedTwo Pointers + Sort20m Longest Substring Without RepeatingArrays & StringsMediumcurrentSliding Window15m Minimum Window SubstringArrays & StringsHardlockedSliding Window25m Group AnagramsArrays & StringsMediumlockedHash Map Grouping15m Trapping Rain WaterArrays & StringsHardlockedTwo Pointers25m Reverse Linked ListLinked ListsEasycompletedIterative Reversal8m Merge Two Sorted ListsLinked ListsEasycompletedDummy Head10m Linked List CycleLinked ListsEasycompletedFloyd's Algorithm8m Remove Nth Node From EndLinked ListsMediumcompletedTwo Pointers12m Reorder ListLinked ListsMediumcompletedFind Middle + Reverse + Merge18m Add Two NumbersLinked ListsMediumcurrentCarry Propagation15m Copy List with Random PointerLinked ListsMediumlockedHash Map Clone20m Merge K Sorted ListsLinked ListsHardlockedHeap / Divide & Conquer25m Two SumHash Maps & SetsEasycompletedValue → Index Map8m Valid AnagramHash Maps & SetsEasycompletedCounter Comparison5m Group AnagramsHash Maps & SetsMediumcompletedSorted Key Grouping12m Top K Frequent ElementsHash Maps & SetsMediumcompletedCounter + heapq12m Longest Consecutive SequenceHash Maps & SetsMediumcompletedSet Lookup15m Encode and Decode StringsHash Maps & SetsMediumcompletedLength Prefix10m Subarray Sum Equals KHash Maps & SetsMediumcompletedPrefix Sum + Map15m Isomorphic StringsHash Maps & SetsEasycompletedBi-directional Map8m LRU CacheHash Maps & SetsHardcompletedOrderedDict25m Design HashMapHash Maps & SetsEasycompletedChaining15m Valid ParenthesesStacks & QueuesEasycompletedStack Matching8m Min StackStacks & QueuesMediumcompletedAuxiliary Stack10m Evaluate Reverse Polish NotationStacks & QueuesMediumcompletedOperand Stack10m Daily TemperaturesStacks & QueuesMediumcompletedMonotonic Stack12m Car FleetStacks & QueuesMediumcompletedStack + Sort15m Largest Rectangle in HistogramStacks & QueuesHardcompletedMonotonic Stack25m Sliding Window MaximumStacks & QueuesHardcurrentMonotonic Deque20m Implement Queue using StacksStacks & QueuesEasylockedAmortized Transfer10m Next Greater ElementStacks & QueuesMediumlockedMonotonic Stack12m Invert Binary TreeTrees & GraphsEasycompletedRecursive Swap5m Maximum Depth of Binary TreeTrees & GraphsEasycompletedDFS Base Case5m Same TreeTrees & GraphsEasycompletedParallel DFS5m Level Order TraversalTrees & GraphsMediumcurrentBFS with deque12m Validate BSTTrees & GraphsMediumlockedIn-order Bounds12m Lowest Common AncestorTrees & GraphsMediumlockedRecursive LCA12m Binary Tree Right Side ViewTrees & GraphsMediumlockedBFS Last Node12m Number of IslandsTrees & GraphsMediumlockedGrid DFS/BFS15m Course ScheduleTrees & GraphsMediumlockedTopological Sort18m Word LadderTrees & GraphsHardlockedBFS Shortest Path25m Clone GraphTrees & GraphsMediumlockedDFS + HashMap15m Pacific Atlantic Water FlowTrees & GraphsMediumlockedMulti-source DFS20m Serialize and Deserialize TreeTrees & GraphsHardlockedPreorder + Queue25m Diameter of Binary TreeTrees & GraphsEasylockedDFS Height10m Subtree of Another TreeTrees & GraphsEasylockedRecursive Match10m Binary SearchSorting & Binary SearchEasycompletedClassic bisect5m Search in Rotated Sorted ArraySorting & Binary SearchMediumcompletedModified Binary Search15m Find Minimum in Rotated ArraySorting & Binary SearchMediumcompletedBinary Search Pivot12m Kth Largest ElementSorting & Binary SearchMediumcompletedheapq.nlargest15m Search a 2D MatrixSorting & Binary SearchMediumcurrentFlattened Binary Search12m Find Peak ElementSorting & Binary SearchMediumlockedGradient Binary Search12m Merge IntervalsSorting & Binary SearchMediumlockedSort + Sweep12m Non-overlapping IntervalsSorting & Binary SearchMediumlockedGreedy + Sort15m Meeting Rooms IISorting & Binary SearchMediumlockedHeap + Sort15m Median of Two Sorted ArraysSorting & Binary SearchHardlockedBinary Search Partition30m Count of Smaller Numbers After SelfSorting & Binary SearchHardlockedMerge Sort Variant30m Climbing StairsDynamic ProgrammingEasylockedFibonacci Pattern8m House RobberDynamic ProgrammingMediumlockedSkip/Take12m Coin ChangeDynamic ProgrammingMediumlockedUnbounded Knapsack15m Longest Increasing SubsequenceDynamic ProgrammingMediumlockedPatience Sort / DP15m Word BreakDynamic ProgrammingMediumlockedDP + Set Lookup15m Unique PathsDynamic ProgrammingMediumlocked2D Grid DP10m Decode WaysDynamic ProgrammingMediumlockedString DP12m Longest Common SubsequenceDynamic ProgrammingMediumlocked2D DP Table15m 0/1 KnapsackDynamic ProgrammingMediumlockedClassic Knapsack15m Partition Equal Subset SumDynamic ProgrammingMediumlockedSubset Sum DP15m Edit DistanceDynamic ProgrammingMediumlocked2D DP20m Burst BalloonsDynamic ProgrammingHardlockedInterval DP30m Regular Expression MatchingDynamic ProgrammingHardlocked2D DP30m Longest Palindromic SubstringDynamic ProgrammingMediumlockedExpand Around Center15m SubsetsBacktracking & RecursionMediumlockedInclude/Exclude10m PermutationsBacktracking & RecursionMediumlockedSwap Backtrack12m Combination SumBacktracking & RecursionMediumlockedUnbounded Choices12m Letter Combinations of PhoneBacktracking & RecursionMediumlockedCartesian Product12m Palindrome PartitioningBacktracking & RecursionMediumlockedPartition + Check18m Word SearchBacktracking & RecursionMediumlockedGrid DFS18m N-QueensBacktracking & RecursionHardlockedColumn/Diagonal Sets25m Sudoku SolverBacktracking & RecursionHardlockedConstraint Propagation30m Generate ParenthesesBacktracking & RecursionMediumlockedOpen/Close Count12m Restore IP AddressesBacktracking & RecursionMediumlockedSegmented Backtrack15m Fizz Buzz (Pythonic)Pythonic PatternsEasycompletedList Comprehension5m Matrix TransposePythonic PatternsEasycompletedzip(*matrix)5m Flatten Nested ListPythonic PatternsMediumcompletedyield from10m Running Sum with accumulatePythonic PatternsEasycompleteditertools.accumulate5m Dictionary Merge & UpdatePythonic PatternsEasycompleteddict | operator5m Custom Sort with key=Pythonic PatternsMediumcompletedLambda Keys10m Walrus Operator PatternsPythonic PatternsMediumcurrent:= in loops12m Dataclass vs NamedTuplePythonic PatternsMediumlockedStruct Patterns15m Top K Frequent (Counter)Python Collections & itertoolsMediumcompletedCounter.most_common10m Merge K Sorted (heapq)Python Collections & itertoolsHardcompletedheapq.merge20m Group By Key (defaultdict)Python Collections & itertoolsEasycurrentdefaultdict(list)8m Sliding Window Max (deque)Python Collections & itertoolsHardlockedcollections.deque20m Combinations & ProductsPython Collections & itertoolsMediumlockeditertools.product12m Chain & FlattenPython Collections & itertoolsMediumlockeditertools.chain.from_iterable10m Ordered Window (OrderedDict)Python Collections & itertoolsMediumlockedOrderedDict.move_to_end15m Bisect Insert PatternsPython Collections & itertoolsMediumlockedbisect.insort12m Priority Queue with heapqPython Collections & itertoolsMediumlockedCustom __lt__12m Design URL ShortenerSystem Design BasicsMediumcurrentHashing + DB25m Design Rate LimiterSystem Design BasicsMediumlockedToken Bucket20m Design Key-Value StoreSystem Design BasicsMediumlockedConsistent Hashing25m Design Twitter FeedSystem Design BasicsHardlockedFan-out / Pull30m Design Chat SystemSystem Design BasicsHardlockedWebSocket + Queues30m Design Notification ServiceSystem Design BasicsMediumlockedPub/Sub25m Design File Storage (S3)System Design BasicsHardlockedChunking + Metadata30m Design Search AutocompleteSystem Design BasicsMediumlockedTrie + Ranking25m Design Web CrawlerSystem Design BasicsMediumlockedBFS + Politeness25m Design InstagramSystem Design BasicsHardlockedCDN + Sharding35m Print in Order (Threading)Concurrency & AsyncEasylockedBarrier / Event10m Producer-ConsumerConcurrency & AsyncMediumlockedqueue.Queue15m Dining PhilosophersConcurrency & AsyncMediumlockedLock Ordering20m Async Web ScraperConcurrency & AsyncMediumlockedaiohttp + gather15m Rate-Limited API CallerConcurrency & AsyncMediumlockedasyncio.Semaphore15m Thread-Safe CounterConcurrency & AsyncEasylockedthreading.Lock8m Filtering & Sorting ResultsSQL FundamentalsEasycurrentMCQ — WHERE + ORDER BY5m Write a JOIN QuerySQL FundamentalsEasylockedINNER JOIN10m Aggregation & GROUP BYSQL FundamentalsMediumlockedSUM + HAVING15m Subqueries vs CTEsSQL FundamentalsMediumlockedMCQ — WITH clause10m Window Functions for RankingSQL FundamentalsHardlockedROW_NUMBER + PARTITION BY20m Choosing the Right Field TypeDjango Models Deep DiveEasycurrentMCQ — Field Types3m Complete the Blog Post ModelDjango Models Deep DiveEasylockedIncomplete Code8m Understanding on_delete BehaviourDjango Models Deep DiveMediumlockedMCQ — Relationships3m Fix the Broken Order ModelDjango Models Deep DiveHardlockedFix Buggy Code15m Abstract Base Model with InheritanceDjango Models Deep DiveHardlockedIncomplete Code20m Create a Django Project & AppDjango FundamentalsEasycompletedstartproject / startapp8m Define a Blog Post ModelDjango FundamentalsEasycompletedmodels.Model + fields10m Run & Write MigrationsDjango FundamentalsEasycompletedmakemigrations / migrate8m Register Models in AdminDjango FundamentalsEasycompletedadmin.site.register5m QuerySet Filtering & ChainingDjango FundamentalsMediumcurrent.filter() / .exclude()12m Function-Based Views + URLsDjango FundamentalsMediumlockedpath() + HttpResponse12m Template Rendering & ContextDjango FundamentalsMediumlockedrender() + {% block %}12m Model Relationships (FK, M2M)Django FundamentalsMediumlockedForeignKey / ManyToMany15m Django Forms & ValidationDjango FundamentalsMediumlockedforms.ModelForm15m Class-Based ViewsDjango FundamentalsMediumlockedListView / DetailView15m Install DRF & First SerializerDjango REST FrameworkEasycompletedModelSerializer8m APIView: List & CreateDjango REST FrameworkMediumcompletedAPIView + Response12m ViewSet + Router SetupDjango REST FrameworkMediumcurrentModelViewSet + DefaultRouter12m Nested SerializersDjango REST FrameworkMediumlockedNested relationships15m Token AuthenticationDjango REST FrameworkMediumlockedTokenAuthentication15m Custom PermissionsDjango REST FrameworkMediumlockedIsAuthenticated / custom15m Filtering & SearchDjango REST FrameworkMediumlockeddjango-filter + SearchFilter12m Pagination StrategiesDjango REST FrameworkMediumlockedPageNumber / Cursor10m File Upload EndpointDjango REST FrameworkMediumlockedFileUploadParser15m Testing DRF APIsDjango REST FrameworkMediumlockedAPIClient + fixtures15m Custom MiddlewareDjango Advanced PatternsMediumlockedprocess_request / response15m Django Signals (post_save)Django Advanced PatternsMediumlocked@receiver + post_save12m Custom Management CommandsDjango Advanced PatternsEasylockedBaseCommand.handle()10m Caching with RedisDjango Advanced PatternsMediumlockedcache.set / cache.get15m Celery Task QueueDjango Advanced PatternsHardlocked@shared_task20m Custom User ModelDjango Advanced PatternsMediumlockedAbstractBaseUser18m Database Optimization (select_related)Django Advanced PatternsMediumlockedN+1 query problem12m Django Channels (WebSockets)Django Advanced PatternsHardlockedAsyncConsumer25m Hello World with FastAPIFastAPI FundamentalsEasycompleted@app.get + uvicorn5m Path & Query ParametersFastAPI FundamentalsEasycompletedType annotations8m Request Body with PydanticFastAPI FundamentalsEasycompletedBaseModel10m Response Models & Status CodesFastAPI FundamentalsMediumcompletedresponse_model + 20110m Dependency Injection BasicsFastAPI FundamentalsMediumcurrentDepends()12m CRUD with In-Memory StoreFastAPI FundamentalsMediumlockedPOST / GET / PUT / DELETE15m Error Handling & HTTPExceptionFastAPI FundamentalsMediumlockedraise HTTPException10m Middleware & CORSFastAPI FundamentalsMediumlockedCORSMiddleware10m Background TasksFastAPI FundamentalsMediumlockedBackgroundTasks12m Auto-generated OpenAPI DocsFastAPI FundamentalsEasylocked/docs + /redoc8m SQLAlchemy Model + Engine SetupFastAPI + SQLAlchemyMediumcompleteddeclarative_base()12m Session Dependency InjectionFastAPI + SQLAlchemyMediumcurrentDepends(get_db)12m CRUD Operations with ORMFastAPI + SQLAlchemyMediumlockedsession.add / query15m Alembic MigrationsFastAPI + SQLAlchemyMediumlockedalembic revision --autogenerate15m Relationship Mapping (1:N, M:N)FastAPI + SQLAlchemyMediumlockedrelationship() + back_populates15m Async SQLAlchemy SessionFastAPI + SQLAlchemyHardlockedAsyncSession + create_async_engine18m Pagination & FilteringFastAPI + SQLAlchemyMediumlockedoffset / limit + query params12m Testing with TestClient + DBFastAPI + SQLAlchemyMediumlockedoverride_dependency15m Password Hashing with bcryptFastAPI AuthenticationEasylockedpasslib + CryptContext8m JWT Token CreationFastAPI AuthenticationMediumlockedpython-jose + encode12m OAuth2PasswordBearer FlowFastAPI AuthenticationMediumlockedOAuth2PasswordBearer15m Protected RoutesFastAPI AuthenticationMediumlockedDepends(get_current_user)12m Role-Based Access ControlFastAPI AuthenticationMediumlockedScopes + Security15m Refresh Token PatternFastAPI AuthenticationHardlockedAccess + Refresh tokens18m Rate Limiting MiddlewareFastAPI AuthenticationMediumlockedslowapi12m Basic Model & Field TypesPydantic & Data ValidationEasycompletedstr, int, Optional5m Field Validators (@field_validator)Pydantic & Data ValidationMediumcompleted@field_validator10m Nested ModelsPydantic & Data ValidationMediumcompletedModel composition10m Custom Serialization (model_dump)Pydantic & Data ValidationMediumcurrentmodel_dump / model_json10m Settings with BaseSettingsPydantic & Data ValidationMediumlockedenv vars + .env12m Discriminated UnionsPydantic & Data ValidationHardlockedLiteral + Discriminator15m Generic ModelsPydantic & Data ValidationHardlockedGeneric[T]15m JSON Schema GenerationPydantic & Data ValidationMediumlockedmodel_json_schema()10m Hybrid PropertiesSQLAlchemy Deep DiveMediumlocked@hybrid_property15m Event Listeners (before_insert)SQLAlchemy Deep DiveMediumlockedevent.listen()12m Raw SQL with text()SQLAlchemy Deep DiveMediumlockedsession.execute(text())10m Eager vs Lazy LoadingSQLAlchemy Deep DiveMediumlockedjoinedload / selectinload15m Polymorphic ModelsSQLAlchemy Deep DiveHardlocked__mapper_args__20m Multi-tenancy PatternsSQLAlchemy Deep DiveHardlockedSchema-per-tenant25m Query Profiling & EXPLAINSQLAlchemy Deep DiveMediumlockedecho=True + EXPLAIN12m

Showing 200 of 200 problems