Progress: 9/75
- Two Sum
- Best Time to Buy and Sell Stock
- Contains Duplicate
- Product of Array Except Self
- Maximum Subarray
- Maximum Product Subarray
- Find Minimum in Rotated Sorted Array
- Search in Rotated Sorted Array
- 3Sum
- Container With Most Water
- Sum of Two Integers
- Number of 1 Bits
- Counting Bits
- Missing Number
- Reverse Bits
- Climbing Stairs
- Coin Change
- Longest Increasing Subsequence
- Longest Common Subsequence
- Word Break
- Combination Sum IV
- House Robber
- House Robber II
- Decode Ways
- Unique Paths
- Jump Game
- Clone Graph
- Course Schedule
- Pacific Atlantic Water Flow
- Number of Islands
- Longest Consecutive Sequence
- Alien Dictionary
- Graph Valid Tree
- Number of Connected Components in an Undirected Graph
- Insert Interval
- Merge Intervals
- Non-overlapping Intervals
- Meeting Rooms
- Meeting Rooms II
- Reverse Linked List
- Detect Cycle in a Linked List
- Merge Two Sorted Lists
- Merge k Sorted Lists
- Remove Nth Node From End of List
- Reorder List
- Set Matrix Zeroes
- Spiral Matrix
- Rotate Image
- Word Search
- Longest Substring Without Repeating Characters
- Longest Repeating Character Replacement
- Minimum Window Substring
- Valid Anagram
- Group Anagrams
- Valid Parentheses
- Valid Palindrome
- Longest Palindromic Substring
- Palindromic Substrings
- Encode and Decode Strings
- Maximum Depth of Binary Tree
- Same Tree
- Invert Binary Tree
- Binary Tree Maximum Path Sum
- Binary Tree Level Order Traversal
- Serialize and Deserialize Binary Tree
- Subtree of Another Tree
- Construct Binary Tree from Preorder and Inorder Traversal
- Validate Binary Search Tree - confi
- Kth Smallest Element in a BST
- Lowest Common Ancestor of a Binary Search Tree
- Implement Trie (Prefix Tree)
- Add and Search Word
- Word Search II
- Top K Frequent Elements
- Find Median from Data Stream
- 706. Design HashMap — core data structure
- 705. Design HashSet — core data structure
- 146. LRU Cache — hash map + linked list
- 155. Min Stack — API design
- **380. Insert Delete GetRandom O(1)** — hash map + array modeling
- 981. Time Based Key-Value Store — versioned data
- **622. Design Circular Queue** — queue/ring buffer
- 641. Design Circular Deque — queue/ring buffer
- 707. Design Linked List — pointer/state
- 211. Add and Search Words Data Structure — trie + API design
- **588. Design In-Memory File System** — modeling
- 348. Design Tic-Tac-Toe — clean state/modeling exercise
- 355. Design Twitter — feeds, ranking, timestamps, data modeling
- **1396. Design Underground System** — event tracking + aggregation
- **1797. Design Authentication Manager** — TTL/session expiration logic
- 1166. Design File System — path modeling
- **1244. Design A Leaderboard** — ranking / maps / sorting
- 642. Design Search Autocomplete System — trie + ranking
- 1603. Design Parking System — OOP
- **362. Design Hit Counter** — time-window aggregation