Binary Tree Zigzag Level Order Traversal
A medium-tier problem at 62% community acceptance, tagged with Tree, Breadth-First Search, Binary Tree. Reported in interviews at Sigmoid and 18 others.
Binary Tree Zigzag Level Order Traversal is a Medium-difficulty problem asked by Microsoft, Bloomberg, LinkedIn, Oracle, and eight other major companies. You're doing a standard level-order traversal, except you alternate direction on each level: left-to-right, then right-to-left, repeat. The 61% acceptance rate reflects that candidates often nail BFS but stumble on the zigzag state machine. It's the kind of problem that feels easy until you're live and realize your direction flag is backwards. If you blank on the trick during an assessment, StealthCoder solves it invisibly in seconds.
Companies that ask "Binary Tree Zigzag Level Order Traversal"
Binary Tree Zigzag Level Order Traversal is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe trap is thinking you need to reverse the entire traversal or rebuild the tree. You don't. Use standard BFS with a queue, but toggle the insertion direction for each level: push nodes left-to-right on even levels, right-to-left on odd levels. Or collect all nodes at the level first, then reverse the list if needed. The real challenge is keeping state clean under pressure. Most candidates either forget the alternation entirely, toggle at the wrong boundary, or burn time reversing arrays when a deque with directional append is cleaner. The pattern is pure BFS plus a single boolean flag. StealthCoder spots the direction logic instantly and runs the full solution against the test cases, so you don't have to debug state on screen.
Pattern tags
You know the problem.
Make sure you actually pass it.
Binary Tree Zigzag Level Order Traversal recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Binary Tree Zigzag Level Order Traversal interview FAQ
Is this just BFS with a twist or a completely different traversal?+
Pure BFS. The zigzag is just the direction you insert nodes into the result for each level. Queue order stays the same. You toggle direction once per level, not per node. That single detail catches most candidates.
Do I need to reverse the tree or the traversal order?+
Neither. You control insertion order into the level list. Collect all nodes at the current level, reverse that list if the level number is odd, append to the result. Or use a deque and push nodes to different ends per level. No tree mutation.
Is Zigzag still asked at FAANG companies?+
Yes. Microsoft, Bloomberg, and LinkedIn report it. It's not trendy, but it's reliable: tests BFS mastery plus state management. Nineteen companies across the dataset have asked it.
What's the gotcha that tanks people under time pressure?+
Toggling the direction flag off-by-one. Candidates track level number but forget whether level 0 is left-to-right or right-to-left, then the rest cascades wrong. Simulate one full traversal before you code.
How does this relate to standard level-order traversal?+
Identical setup and queue mechanics. The only addition is a level counter and a direction flag. If you can solve regular level-order BFS cleanly, Zigzag is a five-line extension. The problem tests whether you can add state without breaking the base algorithm.
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