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Hand-written tutorials, ordered as a recommended learning path.

1. 261 Reverse Linked List Walk through Reverse Linked List with iterative pointer flipping and a clean recursive solution, plus complexity and interview talking points. 5 min read →
2. 262 Rotate Image Rotate an n by n matrix 90 degrees in place by transposing and reversing each row. Walkthrough, edge cases, complexity, and interview script. 4 min read →
3. 263 Rotated Search Solve Search in Rotated Sorted Array in O(log n) with modified binary search. Pivot detection, half-decision logic, and interview talking points. 5 min read →
4. 264 Sliding Window Max Solve Sliding Window Maximum in O(n) using a monotonic deque. Step-by-step walkthrough, interview script, and complexity analysis. 5 min read →
5. 265 Spiral Matrix Solve Spiral Matrix with the four-boundary walk pattern. Clean implementation, edge cases for rectangles, complexity, and interview tips. 5 min read →
6. 266 Subsets Generate all subsets of an array using backtracking and iterative bit-mask approaches. Includes complexity analysis and interview script. 6 min read →
7. 267 Top K Frequent Solve Top K Frequent Elements with both a min-heap and a bucket sort approach. Trade-offs, complexity, and interview-ready walkthrough. 5 min read →
8. 268 Two Sum A complete walkthrough of the Two Sum problem. We move from the obvious nested loop to a single-pass hash map and dissect why it works. 6 min read →
9. 269 Trapping Rain Water Solve Trapping Rain Water in linear time and constant space using the two-pointer technique. Brute force, optimal walkthrough, and interview talk track. 5 min read →
10. 270 Valid Anagram A complete walkthrough of the Valid Anagram problem. Compare the sorting approach with the optimal hash map counting solution and learn how to explain it in interviews. 6 min read →
11. 271 Valid Parentheses A clean walkthrough of Valid Parentheses with the optimal stack solution. Covers edge cases, complexity, and how to explain the approach in interviews. 6 min read →
12. 272 Word Break Solve Word Break with bottom-up dynamic programming. Includes brute force, edge cases, complexity analysis, and an interview script. 6 min read →
13. 273 Interview Math The essential math toolkit for interviews: Euclidean GCD, sieve of Eratosthenes, modular exponentiation, modular inverses, and common pitfalls. 7 min read →
14. 274 Segment Tree Learn segment trees for fast range sum, min, and max queries with point updates, including a clean iterative Python implementation. 6 min read →
15. 275 Topological Sort Compare Kahn's BFS-based topological sort with DFS-based postorder, with Python implementations, complexity, and cycle detection. 5 min read →
16. 276 Tries A practical introduction to tries: node structure, insert, search, prefix queries, memory tradeoffs, and classic interview problems like word search. 6 min read →
17. 277 Union-Find Learn the union-find data structure with union by rank and path compression, why it runs in near-O(1) amortized, and how it powers Kruskal and islands. 6 min read →