Loading repository data…
idevion-organisation / repository
dsa-patterns-java
Pattern-based DSA learning in Java for beginners — helping students move from memorizing solutions to identifying patterns, understanding dry runs, analyzing complexity, avoiding mistakes, and practicing step by step.
#beginner-friendly#beginner-friendly-dsa-solutions#dsa#dsa-algorithm#dsa-java#dsa-learning-series
Live repository statistics
★ 5Stars
⑂ 0Forks
◯ 0Open issues
◉ 5Watchers
README preview
DSA Patterns Java
A beginner-friendly repository for learning Data Structures and Algorithms in Java through problem-solving patterns.
Most beginners memorize solutions, but still get stuck on new problems.
This repo helps you understand the pattern behind a question, dry run the logic, analyze complexity, avoid mistakes, and practice step by step.
Memorizing solutions ❌
Identifying patterns ✅
Writing clean Java code ✅
Solving with confidence ✅
Why This Repo?
Most DSA repos show:
Problem → Code → Output
This repo follows:
Concept → Pattern → Example → Dry Run → Complexity → Mistakes → Practice
The goal is simple:
Learn the pattern behind the problem, not just the final code.
Current Learning Track
Array DSA Patterns in Java
We are starting with Arrays, because arrays are the foundation of many important DSA patterns.
arrays/
├── 00-what-is-array/
├── 01-how-to-approach-array-problems/
├── 02-pattern-01-traversal/
└── 03-pattern-02-linear-search/
| Day | Topic | Status |
|---|---|---|
| 1 | What is Array | ✅ Live |
| 2 | How to Approach Array Problems | ✅ Live |
| 3 | Pattern 01: Traversal | ✅ Live |
| 4 | Pattern 02: Linear Search | ✅ Live |
15-Day Array Plan
| Day | Topic | Status |
|---|---|---|
| 1 | What is Array | ✅ Live |
| 2 | How to Approach Array Problems | ✅ Live |
| 3 | Pattern 01: Traversal | ✅ Live |
| 4 | Pattern 02: Linear Search | ✅ Live |
| 5 | Pattern 03: Binary Search | Coming soon |
| 6 | Pattern 04: Two Pointers | Coming soon |
| 7 | Pattern 05: In-place Overwrite | Coming soon |
| 8 | Pattern 06: HashSet / Duplicate Detection | Coming soon |
| 9 | Pattern 07: HashMap Frequency | Coming soon |
| 10 | Pattern 08: Sorting-Based Patterns | Coming soon |
| 11 | Pattern 09: Merge Sorted Arrays | Coming soon |
| 12 | Pattern 10: Fixed Size Sliding Window | Coming soon |
| 13 | Pattern 11: Variable Size Sliding Window | Coming soon |
| 14 | Pattern 12: Prefix Sum | Coming soon |
| 15 | Pattern 13: Prefix Sum + HashMap | Coming soon |
| 16 | Pattern 14: Kadane’s Algorithm | Coming soon |
| 17 | Pattern 15: Stock Profit Pattern | Coming soon |
| 18 | Pattern 16: XOR and Math Formula | Coming soon |
| 19 | Pattern 17: Rotate, Dutch Flag, Product Except Self, Difference Array | Coming soon |
| 20 | Pattern 18: Matrix, Spiral Matrix, Final Checklist | Coming soon |
What You Will Learn
| Skill | Why It Matters |
|---|---|
| Pattern recognition | Know which approach to try |
| Dry run thinking | Understand how code works |
| Complexity analysis | Know if your solution can pass |
| Java implementation | Write clean beginner-friendly code |
| Mistake handling | Avoid common DSA errors |
| Practice flow | Learn in the right order |
How to Use This Repo
Read concept
↓
Understand example
↓
Dry run manually
↓
Check complexity
↓
Read mistakes
↓
Solve practice questions
Before solving, ask:
What is the pattern?
When should I use it?
Can brute force be optimized?
What is the time complexity?
What mistake should I avoid?
In real problems, the question will not say:
Use HashMap
Use Sliding Window
Use Two Pointers
Use Prefix Sum
You need to identify it.
| Question Signal | Pattern to Think |
|---|---|
| Find sum/count/max/min | Traversal |
| Sorted array + target | Binary Search |
| Sorted array + pair sum | Two Pointers |
| Remove elements in-place | In-place Overwrite |
| Duplicates/frequency | HashSet / HashMap |
Subarray of size k | Sliding Window |
| Range sum query | Prefix Sum |
| Maximum subarray sum | Kadane’s Algorithm |
This repo is useful for:
- beginner DSA students
- Java learners
- placement preparation students
- LeetCode / CodeChef / Codeforces beginners
- students who struggle to identify patterns
- learners who want clean revision notes
After Array patterns, this repo can expand into:
| Topic | Focus |
|---|---|
| Strings | Two pointers, frequency, palindrome, substring |
| Linked List | Fast-slow pointer, reversal, cycle detection |
| Stack & Queue | Monotonic stack, next greater element, BFS basics |
| Recursion | Base case, choices, recursion tree |
| Trees | DFS, BFS, height, path problems |
| Graphs | BFS, DFS, shortest path basics |
| Dynamic Programming | Memoization, tabulation, state thinking |
| Java Templates | Reusable problem-solving templates |
Long-term goal:
Build a complete beginner-friendly DSA pattern guide in Java.
Beginner contributions are welcome.
You can help by adding:
- better examples
- dry runs
- Java solutions
- common mistakes
- edge cases
- practice questions
- formatting improvements
- typo fixes
Before contributing:
- keep explanations simple
- write readable Java code
- mention time and space complexity where needed
- do not add copied paid/protected content
Learning Principle
Do not memorize 100 solutions.
Learn the patterns behind them.
Pattern recognition is the real skill in DSA.
Maintained By
Built by Idevion as a beginner-friendly open-source learning initiative. Idevion focuses on helping students grow through learning resources, roadmaps, projects, and open-source collaboration.
Connect With Idevion
Understand Patterns. Write Clean Java. Solve With Confidence.
If this repo helps you, consider starring it and sharing it with beginner DSA learners.