Leetcode #235 Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined
between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

_______6______
/              \
___2__          ___8__
/      \        /      \
0      _4       7       9
/  \
3   5

For example, the lowest common ancestor (LCA) of nodes

2

and

8

is

6

.
Another example is LCA of nodes

2

and

4

is

2

,
since a node can be a descendant of itself according to the LCA definition.

Difficulty: Easy

用递归的方法，从上到下找节点，Python语法不熟悉。。全是CE。。

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

class Solution(object):
def lowestCommonAncestor(self, root, p, q):
"""
:type root: TreeNode
:type p: TreeNode
:type q: TreeNode
:rtype: TreeNode
"""
if (p.val==root.val or q.val==root.val) or (p.val>root.val and q.val<root.val) or (p.val<root.val and q.val>root.val):
return root
elif p.val<root.val and q.val<root.val:
return self.lowestCommonAncestor(root.left,p,q)
elif p.val>root.val and q.val>root.val:
return self.lowestCommonAncestor(root.right,p,q)