二叉树的递归后继函数(Python)

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

def find_successor(root, target):
    if not root:
        return None
    
    if root.val == target:
        if root.right:
            # 如果目标节点有右子树，则后继节点为右子树中最左边的节点
            node = root.right
            while node.left:
                node = node.left
            return node
        else:
            # 如果目标节点没有右子树，则后继节点为第一个比目标节点大的父节点
            successor = None
            node = root
            while node != target:
                if node.val > target:
                    successor = node
                    node = node.left
                else:
                    node = node.right
            return successor
    
    if root.val > target:
        return find_successor(root.left, target)
    else:
        return find_successor(root.right, target)