1. # Definition for a binary tree node.
    2. # class TreeNode:
    3. #     def __init__(self, x):
    4. #         self.val = x
    5. #         self.left = None
    6. #         self.right = None
    8. class Solution:
    9.     def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
    10.         if root == None or root == p or root == q:
    11.             return root
    13.         left = self.lowestCommonAncestor(root.left, p, q)
    14.         right = self.lowestCommonAncestor(root.right, p, q)
    16.         if left != None and right != None:
    17.             return root
    18.         if left != None:
    19.             return left
    20.         if right != None:
    21.             return right
    22.         return None