Leetcode日练笔记38 [二叉树专题] #102 Binary Tree Level Order Traversal
#102BinaryTreeLevelOrderTraversalGiventherootofabinarytree,returnthelevelordertraversalofitsnodes'values.(i.e.,fromlefttoright,levelbylevel).Example1:Input:root=[3,9,20,null,null,15,7]Output:[[3],[9,2