# 0968. Binary Tree Cameras

<https://leetcode.com/problems/binary-tree-cameras>

## Description

You are given the `root` of a binary tree. We install cameras on the tree nodes where each camera at a node can monitor its parent, itself, and its immediate children.

Return *the minimum number of cameras needed to monitor all nodes of the tree*.

**Example 1:**

![](https://assets.leetcode.com/uploads/2018/12/29/bst_cameras_01.png)

```
**Input:** root = [0,0,null,0,0]
**Output:** 1
**Explanation:** One camera is enough to monitor all nodes if placed as shown.
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2018/12/29/bst_cameras_02.png)

```
**Input:** root = [0,0,null,0,null,0,null,null,0]
**Output:** 2
**Explanation:** At least two cameras are needed to monitor all nodes of the tree. The above image shows one of the valid configurations of camera placement.
```

**Constraints:**

* The number of nodes in the tree is in the range `[1, 1000]`.
* `Node.val == 0`

## ac

```java
```