Binary Tree Cameras
Asked in the Round 1 stage. 1 Hard problem in Round 1.
Given a binary tree, place cameras on the minimum number of nodes so every node is monitored. A camera monitors its node, its parent, and its immediate children.
Represent a tree as nested arrays [value, left, right], where an absent child is null. Implement min_camera_cover(root) and return the minimum camera count.
def min_camera_cover(root):