Amazon Hard Problems sorted by frequency

1. Trapping Rain Water
2. Merge k Sorted Lists
3. Candy
4. Median of Two Sorted Arrays
5. Minimum Window Substring
6. Basic Calculator
7. LFU Cache
8. Concatenated Words
9. Reverse Nodes in k-Group
10. Longest Valid Parentheses
11. Sudoku Solver
12. N-Queens
13. Word Ladder
14. Word Search II
15. Sliding Window Maximum
16. Alien Dictionary
17. Integer to English Words
18. Find Median from Data Stream
19. Longest Increasing Path in a Matrix
20. Design In-Memory File System
21. Basic Calculator III
22. Making A Large Island
23. Stream of Characters
24. Parsing A Boolean Expression
25. Maximum Profit in Job Scheduling
26. Word Break II
27. Maximal Rectangle

Category Based on DS:

📊 Heap / Priority Queue / Sliding Window

1. Sliding Window Maximum
2. LFU Cache
3. Find Median from Data Stream
4. Maximum Profit in Job Scheduling

🧠 Dynamic Programming

1. Candy
2. Word Break II
3. Maximal Rectangle
4. Longest Increasing Path in a Matrix
5. Minimum Window Substring

🔁 Two Pointers / Arrays

1. Trapping Rain Water
2. Median of Two Sorted Arrays

🔡 String Manipulation / Parsing

1. Basic Calculator
2. Basic Calculator III
3. Integer to English Words
4. Parsing A Boolean Expression
5. Concatenated Words
6. Stream of Characters

🔍 Backtracking

1. Sudoku Solver
2. N-Queens
3. Word Search II
4. Reverse Nodes in k-Group
5. Longest Valid Parentheses

🌐 Graph / Topological Sort / BFS / DFS

1. Word Ladder
2. Alien Dictionary
3. Making A Large Island

🧱 System Design / Simulation

1. Design In-Memory File System
2. Merge k Sorted Lists