LintCode:最近公共祖先

"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
import copy
class Solution:
"""
@param root: The root of the binary search tree.
@param A and B: two nodes in a Binary.
@return: Return the least common ancestor(LCA) of the two nodes.
"""
def lowestCommonAncestor(self, root, A, B):
# write your code here
if root == None:
return None
if root == A or root == B:
return root

left = self.lowestCommonAncestor(root.left, A, B)
right = self.lowestCommonAncestor(root.right, A, B)

if left and right:
return root
elif left:
return left
elif right:
return right
else:
return None