Python DSA Interview Prep

⭐ Star this repo if it helps you crack your interview!

98 curated problems · 15 topics · Interview-focused patterns · Python 3

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📖 Guides

Resource	Purpose
🌐 Visual Index	Browse all problems in a filterable UI
PATTERNS.md	Signal → technique cheat-sheet — "which pattern do I use?"
DATA_STRUCTURES.md	Requirement → data-structure chooser

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✅ 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.

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📚 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)

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🗂️ 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

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🎯 How to Use

1. Clone the repository

   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.

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💡 Problem Markers

• _IMP — Important priority picks for interview revision.
• Regular files — Core problems for building solid fundamentals.

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📖 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.

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🤝 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 for more details.

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📝 License

MIT — free to use for learning and interview preparation.

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👨‍💻 Author

Achal Jain · github.com/Achal13jain

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Last updated: June 2026