- Valid Anagram (Easy)
- Longest Substring Without Repeating Characters (Medium)
- Group Anagrams (Medium)
- Maximum Depth of Binary Tree (Easy)
- Binary Tree Level Order Traversal (Medium)
- Validate Binary Search Tree (Medium)
- Kth Largest Element in an Array (Medium)
- Merge k Sorted Lists (Hard)
- Find Median from Data Stream (Hard)