Lowest Common Ancestor of a Binary Search Tree——Tree

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于 2016-08-15 00:12:13 发布

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分类专栏： Leecode Python

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本文介绍了一种在二叉搜索树(BST)中寻找两个指定节点的最低公共祖先(LCA)的方法。根据定义，最低公共祖先是指位于这两个节点间的最近的共同祖先节点。文章提供了一个具体的解决方案，并通过递归方式实现该算法。

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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

# 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
        """
        minNum = p.val if p.val <= q.val else q.val
        maxNum = p.val if p.val > q.val else q.val
        if maxNum < root.val:
            return self.lowestCommonAncestor(root.left, p, q)
        if minNum > root.val:
            return self.lowestCommonAncestor(root.right, p, q)
        return root.val