235. 二叉搜索树的最近公共祖先

类似题：https://www.cnblogs.com/panweiwei/p/13585987.html

class Solution(object):
    def lowestCommonAncestor(self, root, p, q):
        """
        :type root: TreeNode
        :type p: TreeNode
        :type q: TreeNode
        :rtype: TreeNode
        """
        # 先特判
        if not root:
            return None
        if p.val == q.val:
            return p
        # 再遍历
        while root:
            if p.val < root.val and q.val < root.val:
                root = root.left
            elif p.val > root.val and q.val > root.val:
                root = root.right
            else:
                return root