# 236. Lowest Common Ancestor of a Binary Tree

## Description

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).”

Given binary search tree: `root = [6,2,8,0,4,7,9,null,null,3,5]`

``````       _______6______
/              \
___2__          ___8__
/      \        /      \
0      _4       7       9
/  \
3   5
``````

Example 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.

Example 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.

• All of the nodes' values will be unique.
• `p` and `q` are different and both values will exist in the BST.

Tags: Binary Search Tree (BST)

## 题意

### 思路1

``````func Lowest(root *TreeNode, p *TreeNode, q *TreeNode) *TreeNode {
if p.val < root.val && q.val < root.val {
return Lowest(root.left, p, q)
}
if p.val > root.val && q.val > root.val {
return Lowest(root.right, p, q)
}
return root
}
``````