Problem Set

70 Curated Interview Challenges • Live LeetCode Sync • In-Browser Execution

Your Progress

0/ 70 Solved

XP Earned

+0 XP

50 XP per accepted submission

Badges Claimed

Mastery badges unlocked

Sandbox Engine

V8 + Pyodide Worker

Zero server lag • 0ms local

Upgrade to Arena ProFAANG & Unicorn Packs

Unlock company-tagged challenges (Google, Amazon, Swiggy, Uber), AI code explanations, mock OA simulators, and direct recruiter referral fast-tracking.

Topic:

Company OA:

#1Two Sum: Target Pair IndexerEasyArrays & Hashing

Used in financial order book matching at Zerodha and Razorpay to instantaneously pair matching buy and sell prices with O(n) hash map lookups.

Asked in:GoogleAmazonMicrosoftSwiggy

53.2%

#2Valid Parentheses: Syntax Tree ValidatorEasyStack

Directly used in compilers and AST parsers (such as Babel, SWC, and TypeScript compiler) to validate code syntax before compilation.

Asked in:AmazonMicrosoftGoogleBloomberg

41.1%

#3Best Time to Buy & Sell Stock: Volatility Profit TrackerEasyArrays & Hashing

Algorithmic trading engines at Jane Street and Citadel analyze historical asset windows to execute high-frequency arbitrage trades.

Asked in:AmazonGoogleSwiggyGoldman Sachs

54.6%

#4Maximum Subarray: Kadane's AlgorithmMediumDynamic Programming

Used in computer vision (finding highest-contrast regions in an image) and genomic sequence alignment to locate protein coding regions.

Asked in:GoogleAmazonMicrosoft

50.4%

#5Contains Duplicate: Set Collision DetectorEasyArrays & Hashing

Primary deduplication routine in distributed message queues (Kafka, AWS SQS) and unique user identifier validations in PostgreSQL.

Asked in:AmazonAppleAdobeSwiggy

61.3%

#6Valid Anagram: Frequency CounterEasyArrays & Hashing

Employed in spell checkers, text comparison tools, and linguistic cryptanalysis engines.

Asked in:UberGoogleAmazon

63.2%

#7Merge Intervals: Calendar OptimizerMediumIntervals

Google Calendar and Outlook meeting scheduler algorithms collapse free/busy slot blocks to identify overlapping availability across teams.

Asked in:GoogleUberMicrosoftSwiggy

47.1%

#8Binary Search: O(log n) Halving EngineEasyBinary Search

Foundational primitive behind B-Trees, database indexing in Postgres/MySQL, and Git Bisect bug isolation.

Asked in:MicrosoftGoogleAmazonUber

57.8%

#9Vector Cosine Similarity (RAG & Embeddings)EasyAI & Machine Learning

Used in Retrieval-Augmented Generation (RAG) and Pinecone/Qdrant vector stores to calculate semantic similarity between user queries and stored chunk embeddings.

Asked in:GoogleAmazonMicrosoftSwiggy

64.8%

#10Stable Softmax & Temperature (LLM Sampling)MediumAI & Machine Learning

Directly implements the final token sampling layer of ChatGPT and Llama-3, translating raw transformer unnormalized log-probabilities into categorical next-token predictions.

Asked in:GoogleAmazonMicrosoftSwiggy

58.1%

#11BPE Token Pair Frequency (Tokenizer Engine)MediumAI & Machine Learning

Core subword vocabulary generation step used by OpenAI's tiktoken and Hugging Face tokenizers.

Asked in:GoogleAmazonMicrosoft

61.3%

#12Flatten Multi-Dimensional Array (DOM & AST Engine)EasyWeb Engineering

Used in React virtual DOM reconciliation, AST compilers (Babel), and CSS-in-JS rule unrolling.

Asked in:GoogleAmazonMicrosoftSwiggy

72.4%

#13Structured Deep Clone (State Immutability)MediumWeb Engineering

Essential for predictable React Redux/Zustand state immutability, undo-redo histories, and form drafts.

Asked in:GoogleAmazonMicrosoftSwiggy

59.3%

#14Token Bucket Rate Limiter (API Gateway)MediumSystem Design

Deployed in Cloudflare WAF and Stripe API Gateways to prevent DDoS and API quota exhaustion.

Asked in:UberSwiggyAmazonGoogle

54.2%

#15Consistent Hashing Ring Lookup (Distributed Sharding)MediumSystem Design

Used by Discord, DynamoDB, and Memcached to distribute billions of cache keys across server nodes with minimal cache invalidation when nodes are added or removed.

Asked in:GoogleAmazonMicrosoftSwiggy

56.7%

#16Product of Array Except SelfMediumArrays & Hashing

Critical in portfolio risk analytics and stock volatility recalculation where removing one asset's variance must be calculated without recomputing full matrix products.

Asked in:AmazonMicrosoftAppleUber

65.4%

#17Top K Frequent Elements: Trending AnalyticsMediumArrays & Hashing

Powers real-time trending hashtags on Twitter/X, popular product counters on Amazon, and hot cache identification at Cloudflare.

Asked in:GoogleAmazonMicrosoftSwiggy

62.8%

#18Longest Consecutive Sequence: O(n) Streak TrackerMediumArrays & Hashing

Used by gaming servers and Habit Tracker platforms like Duolingo to detect longest uninterrupted daily activity streaks without sorting.

Asked in:GoogleAmazonMicrosoftSwiggy

47.5%

#19Valid Palindrome: Clean String SymmetryEasyTwo Pointers

DNA bioinformatics palindrome sequence matching and search query sanitization in Elasticsearch.

Asked in:GoogleAmazonMicrosoftSwiggy

46.3%

#20Container With Most Water: Maximum AreaMediumTwo Pointers

Resource allocation in cloud server auto-scaling bandwidth envelopes and histogram capacity planning.

Asked in:GoogleAmazonMicrosoftSwiggy

55.3%

#21Longest Substring Without Repeating CharactersMediumSliding Window

High-throughput token sliding window parsing in streaming network packets and cryptographic nonces.

Asked in:AmazonMicrosoftGoogleSwiggy

34.8%

#22Climbing Stairs: Dynamic Step CombinationsEasyDynamic Programming

Fibonacci state transition modeling in CPU instruction pipeline scheduling and branch predictor warm-up cycles.

Asked in:AmazonGoogleUber

52.8%

#23House Robber: Non-Adjacent MaximizationMediumDynamic Programming

Energy harvesting schedules in IoT mesh nodes and CPU cache slot conflict resolution without adjacent bank collisions.

Asked in:GoogleAmazonMicrosoft

50.4%

#24Coin Change: Minimum Denomination DPMediumDynamic Programming

Micro-transaction change-making algorithms in Stripe/Cashfree billing gateways and optimal network MTU packet fragmentation.

Asked in:AmazonMicrosoftSwiggyUber

43.7%

#25Search a 2D Matrix: Row-Column Binary SearchMediumBinary Search

B-Tree index leaf page traversal in PostgreSQL and SQLite disk storage engines.

Asked in:GoogleAmazonMicrosoft

49.6%

#26Find Minimum in Rotated Sorted ArrayMediumBinary Search

Locating clock-skew synchronization offsets in distributed consensus nodes (Raft / Paxos) across UTC boundaries.

Asked in:GoogleAmazonMicrosoft

50.1%

#27Number of Islands: 2D Grid BFS/DFSMediumTrees & Graphs

Computer vision connected-component labeling in satellite imaging, autonomous driving road segment detection, and medical tumor segmentation.

Asked in:AmazonGoogleMicrosoftUber

58.9%

#28Scaled Dot-Product Attention (Transformer Engine)HardAI & Machine Learning

The foundational core equation of modern Generative AI driving language generation, image synthesis, and multimodal reasoning.

Asked in:GoogleAmazonMicrosoftSwiggy

42.1%

#293Sum: Triplet Zero Sum BalanceMediumTwo Pointers

Used in financial accounting ledger reconciliation to discover 3-party zero-balance offset loops, and in computational geometry for 3-point collinearity detection.

Asked in:GoogleAmazonMicrosoft

34.1%

#30Daily Temperatures: Monotonic StackMediumStack

Stock ticker breakout prediction and next-higher price signal lookahead in algorithmic trading engines.

Asked in:GoogleAmazonMicrosoft

66.2%

#31Generate Parentheses: Backtracking TreeMediumStack

AST parser generation, mathematical formula validation, and compiler grammar tree construction.

Asked in:GoogleAmazonMicrosoftSwiggy

74.8%

#32Insert Interval: Calendar MergingMediumIntervals

Conflict-free meeting room booking in Google Calendar, schedule compaction in airline reservations, and memory chunk defragmentation.

Asked in:GoogleAmazonMicrosoft

41.8%

#33Reverse Array In-Place: O(1) Memory InversionEasyTwo Pointers

Undo stack history inversion, GPU vertex winding order reversal, and audio sample time-reversal DSP processing.

Asked in:GoogleAmazonMicrosoftSwiggy

84.5%

#34Binary Cross-Entropy Loss (ML Classifier)MediumAI & Machine Learning

Standard loss objective function for logistic regression, binary classification, and transformer reward models in RLHF (Reinforcement Learning from Human Feedback).

Asked in:GoogleAmazonMicrosoftSwiggy

58.4%

#35Trapping Rain Water: Monotonic Elevation TrapHardTwo Pointers

Applied in GIS topographical hydrology modelling and reservoir watershed simulations at Google Maps and Earth Engine to calculate surface water runoff retention.

Asked in:GoogleAmazonMicrosoft

61.2%

#36Median of Two Sorted Arrays: Logarithmic PartitionHardBinary Search

Used in real-time distributed telemetry streams (Kafka / ClickHouse) at Uber and Amazon to compute median latency SLAs across partitioned edge logs without merging them.

Asked in:GoogleMicrosoftAmazon

39.8%

#37Merge k Sorted Lists: Min-Heap MultiplexerHardTrees & Graphs

Core to distributed log aggregation systems (Loki, Elasticsearch, Kafka) at Swiggy and Uber, where time-sorted log shards from k microservices are multiplexed in real-time.

Asked in:AmazonGoogleUber

51.4%

#38Sliding Window Maximum: Monotonic DequeHardSliding Window

Used in High-Frequency Trading order book volatility monitors and streaming audio/video loudness peak meters at Spotify and Amazon.

Asked in:GoogleAmazonSwiggy

46.5%

#39Longest Valid Parentheses: Stack Boundary DPHardStack

Used in compiler frontends (LLVM, V8) and code formatters (Prettier) to locate well-balanced syntactic blocks and isolate bracket parsing errors.

Asked in:MicrosoftGoogleAmazon

34.1%

#40Edit Distance: Levenshtein Matrix DPHardDynamic Programming

Underpins fuzzy search and query autocorrect in Google Search, spellcheckers, and DNA sequence genome alignment algorithms.

Asked in:GoogleUberAmazon

56.2%

#41Largest Rectangle in Histogram: Monotonic Bar StackHardStack

Used in computer vision (optical character recognition, bounding box segmentation) and database query planning for maximal contiguous memory block allocators.

Asked in:GoogleAmazonMicrosoft

44.7%

#42Minimum Window Substring: Frequency Constrained WindowHardSliding Window

Used in streaming network packet sniffers (Wireshark) and security SIEM log parsers (Splunk) to detect intrusion exploit signatures within payload streams.

Asked in:GoogleAmazonMicrosoft

42.8%

#43Word Ladder: BFS Shortest Transform SequenceHardTrees & Graphs

Powers shortest path state machine transitions, mutation evolutionary trees in bioinformatics, and game-solving graph search engines.

Asked in:AmazonGoogleMicrosoft

39.1%

#44Regular Expression Matching: Recursive Wildcard DPHardDynamic Programming

Foundation of regex parser engines in web browsers (V8 JavaScript RegExp engine, WebKit) and lexer tokenizers in compilers.

Asked in:GoogleMicrosoftUber

28.5%

#45Subarray Sum Equals K: Prefix Sum Hash FrequencyMediumArrays & Hashing

Critical in financial audit reconciliations at Stripe and Razorpay to detect exact matched billing transaction sequences in ledger histories.

Asked in:GoogleMetaSwiggy

43.5%

#46Search in Rotated Sorted Array: Displaced Binary SearchMediumBinary Search

Used in ring buffer circular queues, distributed DHT offset lookups, and chronological log partitions.

Asked in:GoogleAmazonMicrosoft

40.9%

#47Rotting Oranges: Multi-Source Grid Wavefront BFSMediumTrees & Graphs

Used in epidemiology contagion spread models, wildfire propagation simulators, and cascading node failure alerts in AWS data center clusters.

Asked in:AmazonUberSwiggy

54.1%

#48Course Schedule: Topological Cycle DetectorMediumTrees & Graphs

Fundamental to package dependency resolvers (npm, cargo, pip), Terraform execution DAGs, and build systems like Bazel.

Asked in:GoogleAmazonUber

47.2%

#49Kth Largest Element in an Array: QuickSelect OrderMediumArrays & Hashing

Used in real-time quantile monitoring, top-k leaderboard rank slicing, and database order limit offset execution.

Asked in:MetaAmazonMicrosoft

66.7%

#50Pacific Atlantic Water Flow: Continental Dual DFSMediumTrees & Graphs

Used in hydrology drainage basin topology, satellite terrain elevation models, and high-water runoff risk assessments.

Asked in:GoogleAmazon

54.9%

#51Network Delay Time: Dijkstra Shortest Path DelayMediumTrees & Graphs

Core to network packet routing (OSPF protocol), latency SLA analysis across AWS microservices, and Uber ETA calculation algorithms.

Asked in:UberGoogleAmazon

53.6%

#52Decode Ways: Numerical Cipher DPMediumDynamic Programming

Used in variable-length prefix code decoders (Huffman coding), telecommunication binary framing, and cryptographic protocol ciphers.

Asked in:AmazonMicrosoftGoogle

34.5%

#53Jump Game II: Minimum Leaps Greedy BFSMediumDynamic Programming

Used in network packet hop minimization, wireless mesh relay optimization, and game engine character navigation pathfinding.

Asked in:AmazonGoogle

45.0%

#54Combination Sum: Backtracking Target ExplorerMediumArrays & Hashing

Used in ATM currency cash disbursement algorithms, shopping cart promotional coupon optimizers, and cloud server resource bin-packing.

Asked in:AmazonGoogleMicrosoft

71.2%

#55Word Break: Dictionary Segmentability DPMediumDynamic Programming

Used in NLP tokenization (Chinese/Japanese text segmentation without spaces), search query keyword splitting, and URL slug parser segmenters.

Asked in:AmazonGoogleMeta

46.2%

#56Longest Increasing Subsequence: Patience SortMediumDynamic Programming

Used in version control delta diff algorithms (Git patience diff), genomic evolutionary sequence alignments, and stock trend momentum indicators.

Asked in:GoogleMicrosoftAmazon

54.6%

#57Unique Paths: Grid Combinatorics DPMediumDynamic Programming

Used in routing layout ASIC chip physical design, Manhattan distance path routing, and combinatorics probability distributions.

Asked in:AmazonGoogleSwiggy

64.1%

#58Permutations: Full State Space ExplorationMediumArrays & Hashing

Used in traveling salesperson route planners, brute-force security keyspace evaluation, and combinatorial scheduling.

Asked in:GoogleAmazonMicrosoft

77.4%

#59Letter Combinations of a Phone Number: T9 KeyboardMediumArrays & Hashing

Used in T9 predictive keyboard typing, vanity phone number generators (e.g. 1-800-FLOWERS), and mnemonic encoding systems.

Asked in:AmazonMicrosoftUber

60.4%

#60Min Cost Climbing Stairs: Dual Step OptimizationEasyDynamic Programming

Underpins energy minimization routes in robotic leg kinematics and network hop battery consumption budgeting.

Asked in:AmazonMicrosoft

65.8%

#61Find Peak Element: Logarithmic Slope SearchMediumBinary Search

Used in digital audio signal peak detection, seismic activity epicenter localization, and gradient ascent local optima finders.

Asked in:GoogleMetaAmazon

45.8%

#62Capacity To Ship Packages Within D Days: Binary Search AnswerMediumBinary Search

Directly powers logistics batch truck dispatching at Amazon and Delhivery to minimize fleet fuel capacity overhead.

Asked in:GoogleAmazonSwiggy

69.5%

#63Maximum Product Subarray: Dual Running ExtremesMediumDynamic Programming

Used in economic compounding yield modeling and signal amplifier cumulative gain chain optimizers.

Asked in:AmazonGoogleMicrosoft

35.1%

#64Gas Station: Circular Circuit Greedy BalanceMediumDynamic Programming

Used in electric vehicle fleet charging waypoint routing, spacecraft orbital propellant burn planning, and circular token transfer networks.

Asked in:AmazonGoogle

45.7%

#65Partition Labels: Greedy Last Occurrence ChunksMediumTwo Pointers

Used in microservice distributed transaction boundary chunking and video stream keyframe chunk segmentation.

Asked in:AmazonGoogle

80.1%

#66Koko Eating Bananas: Monotonic Speed Binary SearchMediumBinary Search

Used in network streaming buffer throughput tuning and batch consumer rate-limiting throttlers.

Asked in:GoogleAmazonUber

50.1%

#67Palindromic Substrings: Center Expansion CounterMediumTwo Pointers

Used in bioinformatic palindrome hairpin loop RNA folding analysis and data compression algorithms.

Asked in:GoogleMicrosoftMeta

68.9%

#68Find All Anagrams in a String: Fixed Frequency WindowMediumSliding Window

Used in cryptographic frequency analysis attacks, gene sequence motif matching, and plagiarism phrase detectors.

Asked in:AmazonGoogleMicrosoft

50.8%

#69Longest Palindromic Substring: Dynamic Symmetry ExpansionMediumTwo Pointers

Used in genomic palindrome sequence identification, DNA restriction enzyme recognition sites, and reversible pattern compression.

Asked in:AmazonMicrosoftGoogle

33.9%

#70Valid Sudoku: 9x9 Bitmask / Hash ValidationMediumArrays & Hashing

Used in constraint satisfaction solvers (SMT solvers, Z3), puzzle verification engines, and bitmask matrix validations.

Asked in:AmazonMicrosoftUber

59.2%