Applied DSA Coding Problems

Data-structures-and-algorithms practice built around real engineering tasks: parsers, query builders, validators, schedulers and caches. Write a solution, run it against the test suite, and see how it performs.

Easy problems

• Validate JSON Array String — JSON, Validation
• Convert Map to JSON String — JSON, Serialization, Map
• Chunk Collection into Groups — Collections, Streams, Partitioning
• Page Calculator on Items-Per-Page Change — Math, Pagination, UX
• Balanced Brackets — Stack, String
• URL Query String Parser — String Parsing, Map, URL
• Retry with Exponential Backoff — Design, Error Handling, Async
• Reverse Words in a String — String, Array, Basics
• Two Sum — Find Pair with Target — Array, HashMap, Searching
• Count Character Frequency — Map, String, Counting
• Remove Duplicates from Sorted Array — Array, Two Pointers, In-place
• Palindrome Checker — String, Two Pointers
• Boundary-Safe Array Access — Array, Edge Cases, Utility

Medium problems

• JSONPath Reader — JSON, String Parsing, Recursion
• Merge Two JSON Objects — JSON, Recursion, Deep Merge
• Construct JSONPath from Arguments — JSON, String Building
• Convert String to Map — String Parsing, Map, Conversion
• Parse CSV Line with Quoted Fields — String Parsing, CSV, State Machine
• Criteria Object Validator — JSON, Recursion, Validation
• Dynamic SQL Query Builder — String Building, SQL, Builder Pattern
• Sort Tables by Foreign Key Order — Graph, Topological Sort, Database
• Email Address Validator — String Parsing, Validation, Regex
• Deep Clone a JSON Object — JSON, Recursion, Deep Copy
• Flatten Nested JSON — JSON, Recursion, Map
• Topological Sort for Task Scheduling — Graph, Topological Sort, BFS
• LRU Cache Implementation — Design, HashMap, Doubly Linked List
• Rate Limiter — Sliding Window Counter — Sliding Window, Design, Concurrency
• Convert Nested Map to Dot-Notation Keys — Recursion, Map, Conversion
• Template String Interpolator — String Parsing, Map, Regex
• Safe Null Navigator — Null Safety, Edge Cases, Optional
• Type Coercion Comparator — Edge Cases, Comparison, Type System
• Thread-Safe Cache — Design, Concurrency, Cache, Locking
• Producer-Consumer Queue — Concurrency, Queue, Blocking, Threads
• File Change Watcher — File IO, Events, Observer Pattern
• Log File Tail Reader — File IO, Streaming, Real-time
• API Paginator — Fetch All Pages — Pagination, Async, API, Iterator
• Webhook Event Dispatcher — Events, API, HTTP, Retry
• Balanced Brackets II — Stack, Parsing

Hard problems

• JSON Diff — Find Differences — JSON, Recursion, Tree Comparison
• Find JSONPath by Key-Value Search — JSON, Recursion, DFS, Stack
• Criteria to SQL Converter — Recursion, SQL, Parsing, Tree
• Logger Pattern Formatter — State Machine, Parsing, Formatting
• Sliding Window Maximum — Sliding Window, Deque, Array
• Validate and Parse Cron Expression — Validation, Parsing, Scheduling
• OAuth Token Manager — Design, Concurrency, API, Auth
• Balanced Brackets III — Stack, Parsing, Compiler Design