# Python DSA Interview Prep ![Python](https://img.shields.io/badge/Python-3.9+-blue?logo=python) ![Problems](https://img.shields.io/badge/Problems-98-success) ![Topics](https://img.shields.io/badge/Topics-15-orange) ![License](https://img.shields.io/badge/License-MIT-green) > **⭐ Star this repo if it helps you crack your interview!** 98 curated problems · 15 topics · Interview-focused patterns · Python 3 --- ## 📖 Guides | Resource | Purpose | |----------|---------| | [🌐 Visual Index](https://dsa-prep-atlas.pages.dev/) | Browse all problems in a filterable UI | | [PATTERNS.md](./PATTERNS.md) | Signal → technique cheat-sheet — "which pattern do I use?" | | [DATA_STRUCTURES.md](./DATA_STRUCTURES.md) | Requirement → data-structure chooser | --- ## ✅ Progress Tracker **Completion: 100% (98 / 98 problems)** | # | Topic | Easy | Medium | Hard | Total | |---|-------|------|--------|------|-------| | 01 | Basic and Maths | 5 | 3 | 0 | 8 | | 02 | Array and Prefix Sum | 8 | 9 | 0 | 17 | | 03 | Strings | 4 | 4 | 1 | 9 | | 04 | Hashing | 1 | 3 | 0 | 4 | | 05 | Two Pointers & Sliding Window | 1 | 1 | 1 | 3 | | 06 | Stack & Queue | 0 | 3 | 1 | 4 | | 07 | Linked List | 3 | 2 | 0 | 5 | | 08 | Trees | 5 | 2 | 2 | 9 | | 09 | Binary Search | 1 | 2 | 2 | 5 | | 10 | Greedy Problems | 1 | 5 | 0 | 6 | | 11 | Dynamic Programming | 2 | 8 | 1 | 11 | | 12 | Graphs | 2 | 5 | 0 | 7 | | 13 | Heap & Priority Queue | 0 | 2 | 2 | 4 | | 14 | Backtracking | 0 | 4 | 1 | 5 | | 15 | Trie | 0 | 1 | 0 | 1 | | | **Total** | **33** | **54** | **11** | **98** | > **Note:** TreeNode.py in the Trees folder is a shared helper class, not a problem. > Counts verified programmatically: 98 solution files across 15 topic folders. --- ## 📚 Topics Covered ### 1. Basic and Maths LCM & GCD · XOR properties · Power and modular exponentiation · Sieve of Eratosthenes · Perfect squares ### 2. Array and Prefix Sum Two Sum · 3Sum · Kadane's (max subarray) · Prefix sum · Product of array except self · Merge sorted arrays · Move zeroes ### 3. Strings Valid parentheses · Longest substring without repeating · Minimum window substring · Longest palindromic substring · Group anagrams ### 4. Hashing Frequency counting · Longest common subsequence (hash) · Custom data structure design · Count distinct elements in window ### 5. Two Pointers & Sliding Window Two sum (sorted) · Max element in sliding window · Maximum consecutive ones ### 6. Stack & Queue Next greater element · Min stack · Largest rectangle in histogram · Rotten Oranges (multi-source BFS) ### 7. Linked List Reverse · Loop detection (Floyd's) · Merge sorted lists · Middle element · Remove nth from end ### 8. Trees In/Pre/Post-order traversal · Level-order · Height · Diameter · LCA · Path sum · Max path sum · Subtree check · Serialize & Deserialize ### 9. Binary Search Standard binary search · Search in rotated sorted array · Book allocation · Aggressive cows · Peak element ### 10. Greedy Problems Monster battle · Minimum platforms · Job sequencing · Merge intervals · Gas station · Fractional knapsack ### 11. Dynamic Programming Fibonacci · Climbing stairs · Coin change · LIS · LCS · 0/1 Knapsack · Partition equal sum · Max product subarray · Edit distance · Unique paths · House robber ### 12. Graphs BFS template · DFS (recursive + iterative) · Number of Islands · Clone Graph · Course Schedule (topological sort) · Network Delay Time (Dijkstra) · Number of Provinces (Union-Find) ### 13. Heap & Priority Queue Kth largest element · Top K frequent elements · Merge K sorted lists · Find median from data stream ### 14. Backtracking Subsets · Permutations · Combination sum · N-Queens · Word search ### 15. Trie Implement Trie (prefix tree) --- ## 🗂️ Repository Structure ``` ├── 01. Basic and maths/ (8 problems) ├── 02. Array and prefix_sum/ (17 problems) ├── 03. Strings/ (9 problems) ├── 04. Hashing/ (4 problems) ├── 05. Two pointers & Sliding window/ (3 problems) ├── 06. Stack & Queue/ (4 problems) ├── 07. Linked List/ (5 problems) ├── 08. Trees/ (9 problems + TreeNode.py helper) ├── 09. Binary Search/ (5 problems) ├── 10. Greedy Problems/ (6 problems) ├── 11. Dynamic Programming/ (11 problems) ├── 12. Graphs/ (7 problems) ├── 13. Heap and Priority Queue/ (4 problems) ├── 14. Backtracking/ (5 problems) ├── 15. Trie/ (1 problem) ├── index.html — filterable visual index ├── PATTERNS.md — signal → technique cheat-sheet └── DATA_STRUCTURES.md — requirement → data-structure chooser ``` --- ## 🎯 How to Use 1. **Clone the repository** ```bash git clone https://github.com/Achal13jain/Topic-wise-DSA-Imp-questions-Python.git cd Topic-wise-DSA-Imp-questions-Python ``` 2. **Navigate to a topic folder** and open any `.py` file. 3. **Read or run the solution** — some files include a `if __name__ == "__main__":` sample block, and the rest can be tested by calling the function/class directly. 4. **Focus on `_IMP` files** for quick interview prep — these are the priority revision picks in this repo. 5. **Read PATTERNS.md** to recognise which technique to apply when you see a problem signal. --- ## 💡 Problem Markers - **`_IMP`** — Important priority picks for interview revision. - **Regular files** — Core problems for building solid fundamentals. --- ## 📖 Recommended Learning Path ### Beginner ``` Basic and Maths → Array & Prefix Sum → Strings → Hashing ``` ### Intermediate ``` Two Pointers & Sliding Window → Stack & Queue → Linked List ``` ### Advanced ``` Trees → Binary Search → Greedy → Dynamic Programming → Graphs → Heap & Priority Queue → Backtracking → Trie ``` ### Fast-track Interview Prep (2–3 weeks) Focus on all **`_IMP`** files across every topic. They cover the patterns most likely to appear in a 45-minute interview round. --- ## 🤝 Contributing Found an issue or want to improve a solution? 1. Fork the repository 2. Add or improve solutions (match the existing file format) 3. Submit a pull request See [CONTRIBUTING.md](CONTRIBUTING.md) for more details. --- ## 📝 License MIT — free to use for learning and interview preparation. --- ## 👨‍💻 Author **Achal Jain** · [github.com/Achal13jain](https://github.com/Achal13jain) --- *Last updated: June 2026*