Classical Data Structures#

Data Structure Title & Question Number Key Concept / Focus
Hash Table #146 LRU Cache Infra Essential: HashMaps + Doubly Linked Lists for O(1) access/eviction.
Hash Table #460 LFU Cache Advanced eviction policy; frequency-based tracking with nested HashMaps.
Array #1 Two Sum The foundation of frequency mapping and index lookups.
Array #238 Product of Array Except Self Prefix/suffix products without division; common in metric normalization.
String #3 Longest Substring Without Repeating Characters Mastering the Sliding Window pattern.
String #49 Group Anagrams Hashing and grouping; applicable to log deduplication and fingerprinting.
Linked List #206 Reverse Linked List Core pointer manipulation and iterative/recursive logic.
Linked List #23 Merge K Sorted Lists Heap-based merging; mirrors merging sorted log streams from multiple sources.
Stack #20 Valid Parentheses Linear parsing and LIFO (Last-In-First-Out) logic.
Stack #84 Largest Rectangle in Histogram Monotonic stack; useful for capacity planning and resource window analysis.
Queue #239 Sliding Window Maximum Monotonic Queue for optimized window processing.
Queue #933 Number of Recent Calls Rate limiting simulation; directly models request throttling logic.
Tree #102 Binary Tree Level Order Traversal The “Hello World” of Breadth-First Search (BFS).
Tree #236 Lowest Common Ancestor of a Binary Tree Recursive tree traversal; models namespace/path hierarchy resolution.
BST #98 Validate Binary Search Tree Understanding recursion boundaries and tree properties.
BST #230 Kth Smallest Element in a BST In-order traversal; useful for percentile queries on ordered metrics.
Heap #215 Kth Largest Element in an Array Efficiently managing “Top K” streaming data or task priority.
Heap #295 Find Median from Data Stream Dual-heap pattern; real-time percentile tracking (p50/p99 latency).
Graph #200 Number of Islands Matrix traversal using DFS/BFS; the most common graph prompt.
Graph #133 Clone Graph BFS/DFS with memoization; models deep-copying distributed config graphs.
Trie #208 Implement Trie (Prefix Tree) Efficient string prefix storage and autocomplete logic.
Trie #212 Word Search II Trie + DFS backtracking; models multi-pattern log/path matching.
Union-Find #547 Number of Provinces Infra Essential: Models network partition detection and cluster connectivity.
Union-Find #684 Redundant Connection Cycle detection in graphs; identifies redundant links in network topology.

Classical Algorithms#

Algorithm Category Title & Question Number Real-World Context (Infra/SRE)
Binary Search #33 Search in Rotated Sorted Array Searching through partitioned or sharded sorted data sets.
Binary Search #153 Find Minimum in Rotated Sorted Array Efficiently locating boundaries in rotated/partitioned data.
BFS (Graph) #127 Word Ladder Finding the shortest path in an unweighted state-space/network.
BFS (Graph) #994 Rotting Oranges Multi-source BFS; models failure/alert propagation across a network.
DFS (Graph) #207 Course Schedule Topological Sort: Resolving service or package dependencies.
DFS (Graph) #399 Evaluate Division Weighted graph traversal; models unit conversion chains and metric ratios.
Dijkstra #743 Network Delay Time Directly mirrors network packet routing and latency calculations.
Dijkstra #787 Cheapest Flights Within K Stops Constrained shortest path; models cost-aware routing with hop limits.
Two Pointers #15 3Sum Optimizing multi-variable searches from O(n³) to O(n²).
Two Pointers #11 Container With Most Water Greedy boundary shrinking; models capacity optimization problems.
Sliding Window #76 Minimum Window Substring Extracting specific patterns from high-velocity log streams.
Sliding Window #438 Find All Anagrams in a String Fixed-size window pattern matching; applicable to network signature detection.
Backtracking #46 Permutations Exhaustive state-space search (e.g., finding all possible config combinations).
Backtracking #79 Word Search DFS + backtracking on a grid; models path finding in topology graphs.
Greedy #435 Non-overlapping Intervals Infra Essential: Scheduling maintenance windows and minimizing overlapping deploys.
Greedy #55 Jump Game Local decision-making to reach a global destination efficiently.
DP (1D) #322 Coin Change Optimization problems like fitting tasks into fixed-size nodes.
DP (1D) #300 Longest Increasing Subsequence Modeling monotonically growing metrics; version ordering.
DP (2D) #1143 Longest Common Subsequence Underlying logic for diff tools and version control comparisons.
DP (2D) #72 Edit Distance Minimum edit operations; powers fuzzy log matching and config drift detection.
Bit Manipulation #191 Number of 1 Bits Low-level performance tuning and flag-based state management.
Bit Manipulation #136 Single Number XOR-based deduplication; detecting unique anomalies in paired datasets.

Infra System Design in Code#

Storage Systems#

# Problem Infra Scenario
588 Design In-Memory File System File system (mkdir, ls, read, write)
1166 Design File System Hierarchical key-value storage
981 Time Based Key-Value Store Versioned KV store (like MVCC)
1146 Snapshot Array Copy-on-write / snapshot semantics
635 Design Log Storage System Log storage with timestamp range queries
706 Design HashMap Core KV store — hashing, collision resolution
2502 Design Memory Allocator alloc(size) / free(id) — memory allocator

Scheduling / Task Systems#

# Problem Infra Scenario
621 Task Scheduler CPU scheduling with cooldown
1834 Single-Threaded CPU Single-threaded job queue with priority
1882 Process Tasks Using Servers Weighted load-balanced task queue
253 Meeting Rooms II Minimum resources for overlapping jobs

Caching / Eviction#

# Problem Infra Scenario
146 LRU Cache LRU eviction (Redis, Memcached)
460 LFU Cache Frequency-based eviction
1797 Design Authentication Manager Token lifecycle with TTL expiration

Monitoring / Metrics / Rate Limiting#

# Problem Infra Scenario
362 Design Hit Counter QPS tracking, sliding window counter
359 Logger Rate Limiter Log throttling / deduplication
295 Find Median from Data Stream Real-time P50/P99 latency
346 Moving Average from Data Stream Rolling average (CPU, latency)
1825 Finding MK Average Trimmed mean (remove outliers)
933 Number of Recent Calls Fixed-window rate counter
2034 Stock Price Fluctuation Live min/max/current dashboard

Message Queues / Streaming#

# Problem Infra Scenario
1188 Design Bounded Blocking Queue Producer-consumer with backpressure
622 Design Circular Queue Ring buffer (Kafka, Disruptor internals)
641 Design Circular Deque Work-stealing queue
1656 Design an Ordered Stream In-order delivery from out-of-order stream (TCP reassembly)
352 Data Stream as Disjoint Intervals Stream compaction / range merging

Concurrency#

# Problem Infra Scenario
1114 Print in Order Sequential pipeline stages
1115 Print FooBar Alternately Producer-consumer sync
1117 Building H2O Barrier synchronization
1226 The Dining Philosophers Deadlock avoidance
1242 Web Crawler Multithreaded Concurrent worker pool
1279 Traffic Light Controlled Intersection Mutual exclusion

Search / Indexing#

# Problem Infra Scenario
642 Design Search Autocomplete System Typeahead / autocomplete
211 Design Add and Search Words Wildcard pattern matching in indexes
208 Implement Trie Core prefix index structure

Infra Data Structures#

# Problem Infra Scenario
1206 Design Skiplist LevelDB/RocksDB memtable, Redis sorted set
380 Insert Delete GetRandom O(1) Consistent hashing node selection
432 All O(1) Data Structure Real-time metric tracking
855 Exam Room Uniform distribution / consistent hashing
895 Maximum Frequency Stack Hot-key detection in caching

Resource Management#

# Problem Infra Scenario
379 Design Phone Directory Connection pool / ID allocator
355 Design Twitter Multi-resource system (users, feeds, fan-out)
1797 Design Authentication Manager Session management with TTL

Priority# 

Tier 1 (Must do):
├── 146  LRU Cache
├── 588  In-Memory File System
├── 981  Time Based Key-Value Store
├── 1188 Bounded Blocking Queue
├── 362  Hit Counter
├── 621  Task Scheduler
└── 1206 Design Skiplist

Tier 2 (High value):
├── 460  LFU Cache
├── 2502 Memory Allocator
├── 1242 Web Crawler Multithreaded
├── 295  Median from Data Stream
├── 642  Search Autocomplete
├── 359  Logger Rate Limiter
└── 1656 Ordered Stream

Tier 3 (Nice to have):
├── 355  Design Twitter
├── 1226 Dining Philosophers
├── 1146 Snapshot Array
├── 635  Log Storage System
└── 432  All O(1) Data Structure