You are given the root of a binary tree, return the zigzag level order traversal of its nodes' values. (i.e., from left to right, then right to left for the next level and alternate between).
Example 1:
Input: root = [1,2,3,4,5,6,7]
Output: [[1],[3,2],[4,5,6,7]]Example 2:
Input: root = [1]
Output: [[1]]Constraints:
0 <= number of nodes in the tree <= 2000-100 <= Node.val <= 100