Tree BFS
LC #103Medium
Binary Tree Zigzag Level Order Traversal
Tree BFS
AmazonGoogleMetaBloombergProblem
Return zigzag level order traversal: left→right, then right→left, alternating per level.
treebfsdeque
Constraints
- ›0 ≤ n ≤ 2000
- ›-100 ≤ Node.val ≤ 100
Example
Input
root = [3, 9, 20, null, null, 15, 7]Output
[[3], [20, 9], [15, 7]]Why
L0: left→right [3]. L1: right→left [20,9]. L2: left→right [15,7]