LeetCode: Binary Tree Cameras Solution

1/**
2 * Definition for a binary tree node.
3 * function TreeNode(val, left, right) {
4 *     this.val = (val===undefined ? 0 : val)
5 *     this.left = (left===undefined ? null : left)
6 *     this.right = (right===undefined ? null : right)
7 * }
8 */
9/**
10 * @param {TreeNode} root
11 * @return {number}
12 */
13var minCameraCover = function (root) {
14  let res = 0
15  const covered = new Set()
16  covered.add(null)
17
18  const dfs = (node, parent) => {
19    if (node === null) return
20
21    dfs(node.left, node)
22    dfs(node.right, node)
23
24    if (
25      (parent === null && !covered.has(node)) ||
26      !covered.has(node.left) ||
27      !covered.has(node.right)
28    ) {
29      res++
30      covered.add(parent)
31      covered.add(node)
32      covered.add(node.left)
33      covered.add(node.right)
34    }
35  }
36
37  dfs(root, null)
38
39  return res
40}