算法: 二叉树级顺序遍历 (3种解法)102. Binary Tree Level Order Traversal102. Binary Tree Level Order Traversal1. BFS广度优先 解法一2. BFS 简化解法二3. BFS 简化解法三参考
102. Binary Tree Level Order TraversalGiven the root of a binary tree, return the level order traversal of its nodes’ values. (i.e., from left to right, level by level).Example 1:Input: root = [3,9,20,null,null,15,7]Output: [[3],[9,20],[15,7]]Exampl