Medium · Trees
Binary Tree Zigzag Level Order Traversal
Given the root of a binary tree, return its zigzag level order traversal: one row per level, with level 0 read left to right, level 1 right to left, and alternating after that; an empty tree returns [].
Examples
Example 1
[3,9,20,null,null,15,7]Output: [3] [20,9] [15,7]
Example 2
[1,2,3,4,5,6,7]Output: [1] [3,2] [4,5,6,7]
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