297. Serialize and Deserialize Binary Tree
https://leetcode-cn.com/problems/serialize-and-deserialize-binary-tree/solution/shou-hui-tu-jie-gei-chu-dfshe-bfsliang-chong-jie-f/
https://leetcode-cn.com/problems/serialize-and-deserialize-binary-tree/solution/shou-hui-tu-jie-gei-chu-dfshe-bfsliang-chong-jie-f/