added dsa sheet

docs/data-structure-algorithms/dsa-prepsheet.md

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+---
+id: dsa-prepsheet
+title: DSA Practice Sheet
+sidebar_label: DSA Practice Sheet
+sidebar_position: 2
+---
+
+#  DSA Practice Sheet
+
+Welcome to your comprehensive DSA Practice Sheet. Below are **30** carefully curated algorithm and data structure practice questions, grouped by topic and difficulty. Each links to its LeetCode problem. Use the filters at the top to jump right into **Beginner**, **Intermediate**, or **Advanced**.
+
+---
+
+##  Filters
+
+To quickly find questions by difficulty, use these links:
+
+- [Beginner](#beginner)  
+- [Intermediate](#intermediate)  
+- [Advanced](#advanced)  
+
+---
+
+##  Beginner
+
+1. Two Sum – **Array** – [LeetCode](https://leetcode.com/problems/two-sum/)  
+2. Reverse String – **String** – [LeetCode](https://leetcode.com/problems/reverse-string/)  
+3. Valid Parentheses – **Stack** – [LeetCode](https://leetcode.com/problems/valid-parentheses/)  
+4. Merge Two Sorted Lists – **Linked List** – [LeetCode](https://leetcode.com/problems/merge-two-sorted-lists/)  
+5. Maximum Subarray – **Arrays / Kadane's** – [LeetCode](https://leetcode.com/problems/maximum-subarray/)  
+6. Climbing Stairs – **DP (simple)** – [LeetCode](https://leetcode.com/problems/climbing-stairs/)  
+7. Best Time to Buy and Sell Stock – **Array / Greedy** – [LeetCode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)  
+8. Symmetric Tree – **Tree** – [LeetCode](https://leetcode.com/problems/symmetric-tree/)  
+9. Path Sum – **Tree** – [LeetCode](https://leetcode.com/problems/path-sum/)  
+10. Intersection of Two Arrays II – **Hash Table** – [LeetCode](https://leetcode.com/problems/intersection-of-two-arrays-ii/)
+
+---
+
+##  Intermediate
+
+11. Add Two Numbers – **Linked List** – [LeetCode](https://leetcode.com/problems/add-two-numbers/)  
+12. Count and Say – **String / Recursion** – [LeetCode](https://leetcode.com/problems/count-and-say/)  
+13. Binary Tree Inorder Traversal – **Tree / Stack** – [LeetCode](https://leetcode.com/problems/binary-tree-inorder-traversal/)  
+14. Longest Substring Without Repeating Characters – **Sliding Window** – [LeetCode](https://leetcode.com/problems/longest-substring-without-repeating-characters/)  
+15. Container With Most Water – **Two Pointers** – [LeetCode](https://leetcode.com/problems/container-with-most-water/)  
+16. 3Sum – **Two Pointers** – [LeetCode](https://leetcode.com/problems/3sum/)  
+17. Letter Combinations of a Phone Number – **Backtracking** – [LeetCode](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)  
+18. Word Search – **Backtracking** – [LeetCode](https://leetcode.com/problems/word-search/)  
+19. Coin Change – **DP (classic)** – [LeetCode](https://leetcode.com/problems/coin-change/)  
+20. Number of Islands – **DFS / BFS** – [LeetCode](https://leetcode.com/problems/number-of-islands/)
+
+---
+
+##  Advanced
+
+21. Merge k Sorted Lists – **Heap** – [LeetCode](https://leetcode.com/problems/merge-k-sorted-lists/)  
+22. Maximum Subarray Sum with Size K (sliding window variant) – [LeetCode](https://leetcode.com/problems/maximum-subarray-sum-with-size-k/)  
+23. Trapping Rain Water – **Two Pointers** – [LeetCode](https://leetcode.com/problems/trapping-rain-water/)  
+24. Serialize and Deserialize Binary Tree – **Tree / Design** – [LeetCode](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)  
+25. LRU Cache – **Design** – [LeetCode](https://leetcode.com/problems/lru-cache/)  
+26. Word Ladder – **BFS / Graph** – [LeetCode](https://leetcode.com/problems/word-ladder/)  
+27. Longest Consecutive Sequence – **Union-Find or Hash** – [LeetCode](https://leetcode.com/problems/longest-consecutive-sequence/)  
+28. Subarray Sum Equals K – **Hash** – [LeetCode](https://leetcode.com/problems/subarray-sum-equals-k/)  
+29. Minimum Window Substring – **Sliding Window** – [LeetCode](https://leetcode.com/problems/minimum-window-substring/)  
+30. N-Queens – **Backtracking** – [LeetCode](https://leetcode.com/problems/n-queens/)
+
+---
+
+Happy practicing — you've got this.