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:
Input: [0,0,null,0,0] Output: 1 Explanation: One camera is enough to monitor all nodes if placed as shown.
Example 2:
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:
<li>The number of nodes in the given tree will be in the range <code>[1, 1000]</code>.</li>
<li><strong>Every</strong> node has value 0.</li>