Binary Tree Zigzag Level Order Traversal
Given the root of a binary tree, return the zigzag level order traversal of its nodes' values.
The traversal should alternate directions by level:
- Left to right for the first level.
- Right to left for the next level.
- Continue alternating between directions for each subsequent level.
Example 1
3
/ \
9 20
/ \
15 7Input
root = [3,9,20,null,null,15,7]Output
[[3],[20,9],[15,7]]The root level is traversed left to right as
[3], the next level right to left as [20, 9], and the final level left to right as [15, 7].Example 2
1
Input
root = [1]Output
[[1]]The tree has only one node, so the traversal contains a single level with value
1.Constraints
- The number of nodes in the tree is in the range
[0, 2000]. -100 <= Node.val <= 100