/* * function TreeNode(x) { * this.val = x; * this.left = null; * this.right = null; * } */ /** * * @param root TreeNode类 * @return int整型二维数组 */ function levelOrder( root ) { let arr = [] function traversal(root, arr, level) { if(root === null) return if(arr[level] === undefined) arr[level] = [] arr...