刷题记录：二叉树的后序遍历

class Solution:
    def postorderTraversal(self , root: TreeNode) -> List[int]:
        if not root:
            return []
         
        mid = [root.val]
        left = self.postorderTraversal(root.left)
        right = self.postorderTraversal(root.right)
         
        return left + right + mid