1 class TreeNode:
 2     def __init__(self, val=0, left=None, right=None, parent=None):
 3         self.val = val
 4         self.left = left
 5         self.right = right
 6         self.parent = parent
 7 
 8 
 9 def get_left_most(node):
10     if not node:
11         return node
12     while node.left:
13         node = node.left
14     return node
15 
16 def get_successor_node(node):
17     if not node:
18         return node
19     # 如果有右树，则为右子树中最左的节点
20     if node.right:
21         return get_left_most(node.right)
22     else:
23         parent = node.parent
24         # 当前节点是其父节点的右孩子，当前节点可能为最右节点
25         while not parent and parent.left != node:
26             node = parent
27             parent = node.parent
28         return parent