Binary Tree Postorder Traversal

Easy

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

Example 1

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

Example 2

Input:  root = [1,2,3,4,5]
Output: [4,5,2,3,1]

Constraints

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