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* Introducing: Code Playground. You can now solve problems right in DSAForge
204 Java DSA problems with solutions, a code playground and system design
DSA Forge teaches Data Structures and Algorithms in Java, one topic at a time: 185 interview problems and 19 system design case studies, each with a written approach, a full Java solution and its time and space complexity. Now with a code playground: write your solution in the app and run it against real test cases. One finite path you can actually finish, not an endless feed. RUN YOUR JAVA IN THE APP 185 problems come with a built-in code playground. Write your solution in a Java editor with syntax highlighting, run it against the problem's own test cases, and see exactly which cases pass. No IDE, no setup, no pasting code into a compiler website. LEARN DSA IN JAVA, TOPIC BY TOPIC 13 topics, each a complete unit with theory before practice: • Arrays (20 problems): two pointers, sliding window, prefix sums, in-place tricks • Linked Lists (20): fast/slow pointers, cycle detection, reversal, merging • Stacks (20): monotonic stacks, parsing, expression evaluation • Queues (20): deques, circular buffers, BFS, priority queues • Trees (20): DFS and BFS traversal, BSTs, recursion • Graphs (14): BFS, DFS, topological sort, Dijkstra, Union-Find, Bellman-Ford • Sorting (13): merge sort, quicksort, counting and bucket sort, comparators • Searching (13): binary search, binary search on the answer, quickselect • Backtracking (15): subsets, permutations, combinations, pruning • Greedy Algorithms (15): exchange arguments, interval scheduling • Dynamic Programming (15): memoization, tabulation, 1D and 2D DP, knapsack • Low-Level Design (10 case studies): parking lot, elevator, vending machine, LRU cache, expense splitting, logging framework • High-Level Design (9 case studies): URL shortener, rate limiter, news feed, chat, distributed cache, web crawler, ride dispatch, video streaming THEORY BEFORE PRACTICE Every topic opens with how the structure works in memory, key points and interview gotchas, a complexity cheat sheet for each operation, and runnable Java examples: 79 across the app, from a dynamic array built from scratch to Dijkstra with a PriorityQueue. ATTEMPT FIRST, THEN CHECK A problem opens to its statement alone. The approach, the Java solution and the complexity stay hidden until you tap to reveal them, because reading an answer you never attempted teaches you nothing. REAL JAVA, THE WAY INTERVIEWERS EXPECT IT Solutions use the Java Collections Framework the way an interviewer expects: ArrayList, HashMap, HashSet, Deque, PriorityQueue, TreeMap, StringBuilder. If Java is your interview language, you never translate a Python or C++ answer in your head again. SYSTEM DESIGN INTERVIEWS TOO Low-level design with the Strategy, State, Observer, Factory, Singleton and Decorator patterns, and high-level system design covering sharding, consistent hashing, fan-out, message queues, caching and CDNs. TRACK YOUR PROGRESS Tick problems off as you solve them and watch each topic fill up. Finish a topic and get a share card; clear all 204 problems for a certificate of completion. Works without an account, and a free account syncs your progress across devices. NO SIGNUP WALL All 13 topics and all 204 problems are open from the first launch. No lesson gate, no unlock-the-next-topic drip. WHO IT'S FOR • Students preparing for campus placements and coding interviews • Developers targeting SDE 1 and SDE 2 roles at product companies • Anyone revising DSA in Java before a technical round • CS students studying data structures and algorithms for exams • Self-taught programmers who want an ordered path from arrays to DP and system design Start with Arrays. Finish with a certificate.