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# 103. Binary Tree Zigzag Level Order Traversal

## Description

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 = [3,9,20,null,null,15,7]
Output: [[3],[20,9],[15,7]]


Example 2:

Input: root = [1]
Output: [[1]]


Example 3:

Input: root = []
Output: []


Constraints:

• The number of nodes in the tree is in the range [0, 2000].
• -100 <= Node.val <= 100