1. Maximum Path Sum: Implement a function to find the maximum path sum in a binary tree.

2. Serialize and Deserialize: Write a function to serialize and deserialize a binary tree.

3. Kth Smallest Element: Implement a function to find the kth smallest element in a binary search tree (BST).

4. Kth Largest Element: Write a function to find the kth largest element in a BST.

5. Inorder Successor: Implement a function to find the inorder successor of a node in a BST.

6. Inorder Predecessor: Write a function to find the inorder predecessor of a node in a BST.

7. Build Tree from Inorder and Preorder: Implement a function to construct a binary tree from inorder and preorder traversals.

8. Build Tree from Inorder and Postorder: Write a function to construct a binary tree from inorder and postorder traversals.

9. Validate BST: Implement a function to check if a binary tree is a valid BST.

10. Convert BST to Greater Tree: Write a function to convert a BST to a greater tree.

11. Distance Between Nodes: Implement a function to find the distance between two nodes in a binary tree.

12. Nodes at Distance K: Write a function to find all nodes at a distance k from a given node in a binary tree.

13. LCA in BST: Implement a function to find the lowest common ancestor (LCA) of two nodes in a BST.

14. Maximum Width: Write a function to find the maximum width of a binary tree.

15. Vertical Sum: Implement a function to find the vertical sum of a binary tree.

16. Diagonal Sum: Write a function to find the diagonal sum of a binary tree.

17. Path Sum: Implement a function to check if a binary tree has a root-to-leaf path with a given sum.

18. Sum of Nodes with Even-Valued Grandparents: Write a function to find the sum of all nodes with even-valued grandparents in a binary tree.

19. Delete Node in BST: Implement a function to delete a node from a BST.

20. Insert Node in BST: Write a function to insert a node into a BST.

21. Sorted Array to BST: Implement a function to convert a sorted array to a BST.

22. Sorted Linked List to BST: Write a function to convert a sorted linked list to a BST.

23. Good Leaf Node Pairs: Implement a function to find the number of good leaf node pairs in a binary tree.

24. Sum of Nodes on Longest Path: Write a function to find the sum of nodes on the longest path from root to leaf in a binary tree.

25. Smallest Subtree with Deepest Nodes: Implement a function to find the smallest subtree with all the deepest nodes in a binary tree.

26. Recover BST: Write a function to recover a BST where two nodes are swapped by mistake.

27. Count Uni-value Subtrees: Implement a function to count the number of uni-value subtrees in a binary tree.

28. Sum of Nodes in Range: Write a function to find the sum of all nodes' values in a BST within a given range.

29. Deepest Leaves Sum: Implement a function to find the deepest leaves sum in a binary tree.

30. Check Height-Balanced Tree: Write a function to check if a binary tree is height-balanced.