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.

BST，从root处开始，满足公共root的node必为满足值介于两者之间的第一个值

class Solution:

    # @param {TreeNode} root

    # @param {TreeNode} p

    # @param {TreeNode} q

    # @return {TreeNode}

    def lowestCommonAncestor(self, root, p, q):

        while 1:

            if root.val > max(p.val,q.val):

                root = root.left

            elif root.val < min(p.val,q.val):

                root = root.right

            else:

                return root