Given a binary tree, we install cameras on the nodes of the tree.
Each camera at a node can monitor its parent, itself, and its immediate children.
Calculate the minimum number of cameras needed to monitor all nodes of the tree.
Example 1:
![1](https://github.com/imgoogege/LeetCode-in-Go/raw/fe39b3200b40/Algorithms/0968.binary-tree-cameras/1.png)
Input: [0,0,null,0,0]
Output: 1
Explanation: One camera is enough to monitor all nodes if placed as shown.
Example 2:
![2](https://github.com/imgoogege/LeetCode-in-Go/raw/fe39b3200b40/Algorithms/0968.binary-tree-cameras/2.png)
Input: [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.
Note:
- The number of nodes in the given tree will be in the range [1, 1000].
- Every node has value 0.