二叉树--2

https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/
递归方法

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if not root:
            return None
        if root==q or root==p:
            return root#如果节点为目标地址，则返回该节点
        left=self.lowestCommonAncestor(root.left,p,q)
        right=self.lowestCommonAncestor(root.right,p,q)
        if left and right:
            return root#如果节点在左和右都有目标值，则该节点为最近祖先
        return left if left else right