Given the root
of a binary tree, return all root-to-leaf paths in any order.
A leaf is a node with no children.
Example 1:
Input: root = [1,2,3,null,5] Output: ["1->2->5","1->3"]
Example 2:
Input: root = [1] Output: ["1"]
Constraints:
[1, 100]
.-100 <= Node.val <= 100