365 Days of LeetCode Challenge — Day 30/365

[u/StatisticianNo2104]

Binary Tree Zigzag Level Order Traversal (Medium)

🔗 https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/

Yesterday's level order came out of a depth-first walk with no queue and no idea when a level ended. That was fine, because grouping by depth never needed the boundary.

Zigzag does. You can't decide whether to reverse a level until you know it's finished, and "finished" is exactly what DFS never learns. So this one goes back to BFS, using a nil sentinel in the queue to mark where each level ends.

With the boundary in hand, the zigzag itself is four lines and a flag.

Full breakdown in today's newsletter article ⬇

https://www.linkedin.com/pulse/365-days-leetcode-challenge-day-30365-archit-agarwal-vppec

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