968. 监控二叉树 https://leetcode.cn/problems/binary-tree-cameras
968. Binary Tree Cameras https://leetcode.com/problems/binary-tree-cameras
979. 在二叉树中分配硬币 https://leetcode.cn/problems/distribute-coins-in-binary-tree
979. Distribute Coins in Binary Tree https://leetcode.com/problems/distribute-coins-in-binary-tree
1080. 根到叶路径上的不足节点 https://leetcode.cn/problems/insufficient-nodes-in-root-to-leaf-paths
1080. Insufficient Nodes in Root to Leaf Paths https://leetcode.com/problems/insufficient-nodes-in-root-to-leaf-paths
2049. 统计最高分的节点数目 https://leetcode.cn/problems/count-nodes-with-the-highest-score
2049. Count Nodes With the Highest Score https://leetcode.com/problems/count-nodes-with-the-highest-score
写在后序位置的代码是最潇洒的，上通父节点（可以通过函数参数获取父节点信息），下通子树（可以通过递归返回值收集子树信息），有少部分难度比较大的题目会同时用到这两个特性。
