# 236. Lowest Common Ancestor of a Binary Tree

## Description

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: “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]

``````_______3______
/              \
___5__          ___1__
/      \        /      \
6      _2       0       8
/  \
7   4
``````

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 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.

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

Tags: Binary Tree

## 题意

### 思路1

``````type TreeNode struct {
val   int
left  *TreeNode
right *TreeNode
}
``````