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Real-World Applications Index

Reverse mapping from industry domains to algorithmic problems

This guide maps real-world engineering domains to the algorithmic problems that teach relevant concepts. Use it to:

  • Connect your career interests to practice problems
  • Understand why specific algorithms matter in production systems
  • Prepare for domain-specific technical interviews

Quick Navigation

Domain Key Concepts
Database Internals B-trees, LSM trees, indexing, query optimization
Web Development Caching, rate limiting, session management
Operating Systems Scheduling, memory management, process coordination
Distributed Systems Consensus, load balancing, partitioning
Machine Learning Optimization, clustering, similarity
Computer Graphics Geometry, pathfinding, collision detection
Networking Routing, packet processing, encryption
Finance & Trading Real-time processing, time series, risk analysis
Healthcare & Bioinformatics Sequence alignment, pattern matching
DevOps & Infrastructure Resource allocation, monitoring, deployment

Database Internals

For those building: database engines, storage systems, query planners

Indexing & Data Structures

Problem Why It Matters
E001 Two Sum Hash table fundamentals → index lookups, join algorithms
M008 Search in Rotated Sorted Array Binary search variants → B-tree traversal
M556 Time Based Key-Value Store Temporal queries → MVCC, time-travel queries
M015 Maximum Subarray Range queries → aggregate indexes

Sorting & Merging (LSM Trees, Compaction)

Problem Why It Matters
E088 Merge Sorted Array Sorted merge → LSM tree compaction
E021 Merge Two Sorted Lists Merge operations → k-way merge in databases
H023 Merge K Sorted Lists K-way merge → external sorting, SSTable merging

Query Optimization

Problem Why It Matters
M565 Satisfiability of Equality Equations Constraint solving → query optimizer, join ordering
H114 Subarrays with K Different Integers Sliding window → query window functions

Web Development & Backend Systems

For those building: web services, APIs, caching layers

Caching & Rate Limiting

Problem Why It Matters
M556 Time Based Key-Value Store Time-based storage → Redis TTL, cache expiration
E001 Two Sum Hash lookups → cache hits, session stores
M015 Maximum Subarray Streaming max → rate limit windows

Request Processing & Load Balancing

Problem Why It Matters
H009 Trapping Rain Water Capacity analysis → buffer management
M512 Minimize Malware Spread Network analysis → load distribution

URL & String Processing

Problem Why It Matters
M002 Longest Substring Without Repeating Sliding window → URL parsing, text processing
M003 Longest Palindromic Substring String DP → slug generation, validation

Operating Systems & System Programming

For those building: kernels, schedulers, memory managers

Process Scheduling

Problem Why It Matters
M088 Course Schedule Topological sort → dependency resolution, build systems
M015 Maximum Subarray Local vs global optima → scheduling decisions

Memory Management

Problem Why It Matters
H009 Trapping Rain Water Boundary tracking → memory pools, fragmentation
M556 Time Based Key-Value Store Versioned storage → copy-on-write memory

Resource Allocation

Problem Why It Matters
H113 Binary Tree Cameras Minimum coverage → resource placement
M512 Minimize Malware Spread Component analysis → process isolation

Distributed Systems

For those building: microservices, consensus protocols, cloud infrastructure

Network Partitioning & Connectivity

Problem Why It Matters
M565 Satisfiability of Equality Equations Union-Find → network connectivity, cluster discovery
M512 Minimize Malware Spread Connected components → failure domains, blast radius

Consensus & Coordination

Problem Why It Matters
H115 Number of Squareful Arrays Permutation constraints → configuration validation
H116 Maximum Binary Tree II Tree modification → distributed data structure updates

Load Distribution

Problem Why It Matters
H009 Trapping Rain Water Capacity calculation → queue depth management
M015 Maximum Subarray Peak detection → auto-scaling triggers

Machine Learning & Data Science

For those building: ML pipelines, recommendation systems, analytics

Optimization

Problem Why It Matters
M015 Maximum Subarray Local/global optima → gradient descent concepts
H009 Trapping Rain Water Valley detection → anomaly detection in time series

Similarity & Clustering

Problem Why It Matters
E001 Two Sum Complement search → nearest neighbor, similarity matching
M565 Satisfiability of Equality Equations Grouping → clustering, community detection

Feature Engineering

Problem Why It Matters
M015 Maximum Subarray Window features → rolling aggregations
H114 Subarrays with K Different Integers Counting patterns → cardinality estimation

Computer Graphics & Game Development

For those building: game engines, rendering systems, simulations

Physics Simulation

Problem Why It Matters
H009 Trapping Rain Water Water simulation → fluid dynamics approximation
M015 Maximum Subarray Force accumulation → physics calculations

Pathfinding & Navigation

Problem Why It Matters
M512 Minimize Malware Spread Graph traversal → navigation meshes
M088 Course Schedule Dependency graphs → quest/achievement systems

Collision Detection

Problem Why It Matters
E001 Two Sum Spatial hashing → broad-phase collision
H009 Trapping Rain Water Boundary analysis → terrain collision

Networking & Security

For those building: network protocols, security tools, firewalls

Packet Processing

Problem Why It Matters
M556 Time Based Key-Value Store Temporal lookup → packet timestamping, flow tracking
M002 Longest Substring Without Repeating Sliding window → packet window management

Network Analysis

Problem Why It Matters
M512 Minimize Malware Spread Infection propagation → vulnerability assessment
M565 Satisfiability of Equality Equations Constraint validation → firewall rule checking

Cryptography Fundamentals

Problem Why It Matters
E001 Two Sum Hash functions → cryptographic primitives
H115 Number of Squareful Arrays Combinatorial enumeration → key generation

Finance & Trading

For those building: trading systems, risk management, fintech

Real-Time Analysis

Problem Why It Matters
M015 Maximum Subarray Profit windows → best trading intervals
H009 Trapping Rain Water Valley detection → market dip analysis

Time Series Processing

Problem Why It Matters
M556 Time Based Key-Value Store Historical queries → audit trails, compliance
H114 Subarrays with K Different Integers Pattern counting → diversity metrics

Matching Engines

Problem Why It Matters
E001 Two Sum Complement matching → order book matching
H023 Merge K Sorted Lists Priority merging → order queue processing

Healthcare & Bioinformatics

For those building: genomics tools, clinical systems, health analytics

Sequence Alignment

Problem Why It Matters
M003 Longest Palindromic Substring Sequence matching → DNA/RNA pattern finding
M002 Longest Substring Without Repeating Unique sequences → gene identification

Signal Processing

Problem Why It Matters
M015 Maximum Subarray Peak detection → EKG analysis, anomaly detection
H009 Trapping Rain Water Boundary analysis → medical imaging

Clinical Workflows

Problem Why It Matters
M088 Course Schedule Dependency ordering → treatment protocols
H113 Binary Tree Cameras Coverage optimization → sensor placement

DevOps & Infrastructure

For those building: CI/CD pipelines, monitoring systems, cloud tools

Build Systems & Dependencies

Problem Why It Matters
M088 Course Schedule Topological sort → build order, package resolution
M565 Satisfiability of Equality Equations Constraint checking → version compatibility

Monitoring & Alerting

Problem Why It Matters
M015 Maximum Subarray Peak detection → alert thresholds
H009 Trapping Rain Water Capacity analysis → queue depth monitoring
M556 Time Based Key-Value Store Historical metrics → time-series databases

Incident Response

Problem Why It Matters
M512 Minimize Malware Spread Blast radius analysis → incident containment
H113 Binary Tree Cameras Minimum coverage → monitoring agent placement

Civil Engineering & Urban Planning

For those working with: infrastructure design, resource management

Drainage & Water Systems

Problem Why It Matters
H009 Trapping Rain Water Reservoir capacity → stormwater drainage design

Network Design

Problem Why It Matters
H113 Binary Tree Cameras Coverage optimization → surveillance placement
M512 Minimize Malware Spread Connectivity analysis → utility network design

Cross-Domain Patterns

These patterns appear across multiple domains:

Hash Tables (O(1) Lookup)

  • Database: Index lookups, join hash tables
  • Web: Cache hits, session stores
  • Finance: Order matching, symbol lookup
  • Networking: Flow tables, connection tracking

Key Problems: E001 Two Sum, M556 Time Based Key-Value Store

Graph Connectivity (Union-Find)

  • Distributed Systems: Cluster discovery, partition detection
  • Networking: Network segmentation, routing
  • Security: Vulnerability propagation
  • DevOps: Service dependencies

Key Problems: M565 Satisfiability of Equality Equations, M512 Minimize Malware Spread

Sliding Window

  • Web: Rate limiting, session windows
  • Finance: Trading windows, rolling metrics
  • Networking: Packet windows, flow control
  • ML: Feature windows, streaming aggregations

Key Problems: M002 Longest Substring Without Repeating, H114 Subarrays with K Different Integers

Greedy/DP Optimization

  • All domains: Resource allocation, scheduling, capacity planning

Key Problems: M015 Maximum Subarray, H009 Trapping Rain Water, H113 Binary Tree Cameras

How to Use This Guide

Interview Preparation

  1. Identify your target company's domain (e.g., "database company")
  2. Find the relevant section above
  3. Prioritize problems mapped to that domain
  4. Practice explaining the real-world connection

Learning Path by Domain

  1. Database Engineer Track: E001 → M008 → M556 → H023
  2. Backend Engineer Track: E001 → M002 → M556 → M088
  3. ML Engineer Track: E001 → M015 → M565 → H114
  4. Security Engineer Track: E001 → M512 → M565 → H115

When Stuck

If a problem feels abstract, find it in this index and read the real-world context. Understanding why an algorithm matters often makes the how clearer.

Navigation: Main Index | Easy Problems | Medium Problems | Hard Problems