Binary Tree Level Order Traversal

Given the root of a binary tree represented as level-order input (-1 indicates null/empty node), return the level order traversal of its nodes' values (from left to right, level by level). ### Constraints - Number of nodes in the tree is in range `[0, 2000]`. - `-1000 <= Node.val <= 1000` ### Input Format A single line containing space-separated integers representing the level-order traversal of the tree (-1 for null). ### Output Format Print each level on a separate line with space-separated node values. If the tree is empty, print nothing.