class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def traverse(root):
    if not root:
        return
    traverse(root.left)
    traverse(root.right)
    print(root.val, end=" ")

if __name__ == "__main__":
    root = TreeNode(1)
    root.right = TreeNode(2)
    root.right.left = TreeNode(3)

    print("后序遍历结果：", end="")
    traverse(root)