package main

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func minCameraCover(root *TreeNode) int {
	covered := map[*TreeNode]bool{
		nil: true,
	}
	return dfs(root, nil, covered)
}

func dfs(node, parent *TreeNode, covered map[*TreeNode]bool) int {
	if node != nil {
		out := dfs(node.Left, node, covered)
		out += dfs(node.Right, node, covered)

		_, nc := covered[node]
		_, lc := covered[node.Left]
		_, rc := covered[node.Right]
		if parent == nil && !nc || !lc || !rc {
			covered[node] = true
			covered[parent] = true
			covered[node.Left] = true
			covered[node.Right] = true
			return out + 1
		}
		return out
	}
	return 0
}