Binary Tree Inorder Traversal

Easy

Given the root of a binary tree, return its inorder traversal (left, node, right) as a list of values.

Example 1

Input:  root = [1,null,2,3]
Output: [1,3,2]

Example 2

Input:  root = []
Output: []

Constraints

• 0 <= number of nodes <= 100
• -100 <= Node.val <= 100