A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.
The path sum of a path is the sum of the node's values in the path.
Given the `root` of a binary tree, return *the maximum path sum of any path*.
Example 1
Input: root = [1,2,3]
Output: 6
Example 2
Input: root = [-10,9,20,null,null,15,7]
Output: 42
Example 3
Input: root = [-3]
Output: -3
Constraints
•The number of nodes in the tree is in the range [1, 3 * 10⁴].