# [236. Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/)


## 题目

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

According to the [definition of LCA on Wikipedia](https://en.wikipedia.org/wiki/Lowest_common_ancestor): “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 the following binary tree: root = [3,5,1,6,2,0,8,null,null,7,4]

![](https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/12/15/binarytree.png)

**Example 1:**

    Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
    Output: 3
    Explanation: The LCA of nodes 5 and 1 is 3.

**Example 2:**

    Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
    Output: 5
    Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

**Note:**

- All of the nodes' values will be unique.
- p and q are different and both values will exist in the binary tree.

## 题目大意

给定一个二叉树, 找到该树中两个指定节点的最近公共祖先。

百度百科中最近公共祖先的定义为：“对于有根树 T 的两个结点 p、q，最近公共祖先表示为一个结点 x，满足 x 是 p、q 的祖先且 x 的深度尽可能大（一个节点也可以是它自己的祖先）。”


## 解题思路

- 这是一套经典的题目，寻找任意一个二叉树中两个结点的 LCA 最近公共祖先，考察递归