92. Binary Tree Zigzag Level Order Traversal

MediumTree

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).

Examples

Input: [3,9,20,null,null,15,7]

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

Explanation: Level 0 left-to-right, level 1 right-to-left, level 2 left-to-right.

Constraints

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