968.py

# leetcode 968 监控二叉树

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def __init__(self):
        self.res = 0

    def minCameraCover(self, root: Optional[TreeNode]) -> int:

        if self.travel(root) == 0:
            self.res += 1

        return self.res

    def travel(self, cur):
        if not cur:
            return 2

        left = self.travel(cur.left)
        right = self.travel(cur.right)

        if left == 2 and right == 2:
            return 0

        if left == 0 or right == 0:
            self.res += 1
            return 1

        if left == 1 or right == 1:
            return 2