30 Amazon loop-interview LeetCode problems, laid out as a 30-day "WOD" plan. Grouped by the patterns Amazon's bar-raiser rounds hit most. Do one per day, time-box to 30–40 min, then read the editorial.

Day | Problem | Difficulty | Pattern

• 1: Two Sum | Easy | Hash map
• 2: Valid Parentheses | Easy | Stack
• 3: Merge Two Sorted Lists | Easy | Linked list / two pointers
• 4: Best Time to Buy and Sell Stock | Easy | Greedy / running min
• 5: Group Anagrams | Medium | Hash map
• 6: Longest Substring Without Repeating Characters | Medium | Sliding window
• 7: Longest Palindromic Substring | Medium | Expand around center / DP
• 8: Product of Array Except Self | Medium | Prefix/suffix
• 9: Container With Most Water | Medium | Two pointers
• 10: 3Sum | Medium | Sort + two pointers
• 11: Number of Islands | Medium | BFS/DFS grid
• 12: Rotting Oranges | Medium | Multi-source BFS
• 13: Course Schedule | Medium | Topological sort
• 14: Clone Graph | Medium | Graph DFS + hash
• 15: Word Search | Medium | Backtracking
• 16: Kth Largest Element in an Array | Medium | Heap / quickselect
• 17: Top K Frequent Elements | Medium | Heap / bucket sort
• 18: Merge Intervals | Medium | Sort + sweep
• 19: Meeting Rooms II | Medium | Heap / sweep line
• 20: Search in Rotated Sorted Array | Medium | Binary search
• 21: Find Median from Data Stream | Hard | Two heaps
• 22: LRU Cache | Medium | Hash + doubly linked list
• 23: Lowest Common Ancestor of a Binary Tree | Medium | Tree recursion
• 24: Binary Tree Level Order Traversal | Medium | BFS
• 25: Validate Binary Search Tree | Medium | Inorder / bounds
• 26: Coin Change | Medium | DP (unbounded knapsack)
• 27: Word Break | Medium | DP
• 28: Longest Increasing Subsequence | Medium | DP + binary search
• 29: Trapping Rain Water | Hard | Two pointers / stack
• 30: Word Ladder | Hard | BFS shortest path