【练习】运用层序遍历解题 II

919. 完全二叉树插入器 https://leetcode.cn/problems/complete-binary-tree-inserter

872. 叶子相似的树 https://leetcode.cn/problems/leaf-similar-trees

863. 二叉树中所有距离为 K 的结点 https://leetcode.cn/problems/all-nodes-distance-k-in-binary-tree