235. 二叉搜索树的最近公共祖先(lowestCommonAncestor)

# 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):
    res = None

    def lowestCommonAncestor(self, root, p, q):
        """
        :type root: TreeNode
        :type p: TreeNode
        :type q: TreeNode
        :rtype: TreeNode
        """
        self.lock(root, p, q)
        return self.res

    def lock(self, root, p, q):
        if (root.val - p.val)*(root.val - q.val) <= 0:
            self.res = root
        elif p.val < root.val and q.val < root.val:
            self.lock(root.left, p, q)
        else:
            self.lock(root.right, p, q)