0%

### 题目描述

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 p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”

### 例子

#### 例子 1

Input: `root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8`
Output: `6`
Explanation: The LCA of nodes 2 and 8 is 6.

#### 例子 2

Input: `root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4`
Output: `2`
Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

#### 例子 3

Input: `root = [2,1], p = 2, q = 1`
Output: `2`

### Constraints

• The number of nodes in the tree is in the range `[2, 10^5]`.
• `-10^9 <= Node.val <= 10^9`
• All `Node.val` are unique.
• `p != q`
• `p` and `q` will exist in the BST.

### 解题思路

• 时间复杂度: O(n)
• 空间复杂度: O(h)

GitHub 代码同步地址： 235.LowestCommonAncestorOfABinarySearchTree.cpp

GitHub: Leetcode-C++-Solution