Populating Next Right Pointers in Each Node II
A medium-tier problem at 56% community acceptance, tagged with Linked List, Tree, Depth-First Search. Reported in interviews at Snowflake and 2 others.
Populating Next Right Pointers in Each Node II is a medium-difficulty tree problem that shows up in screens at Snowflake, Citadel, and Walmart Labs. It's deceptively simple to state: connect each node to the next node at the same level using a next pointer. The catch is that the input tree is not a perfect binary tree, which kills the elegant math-based solution. About half of candidates accept it on first attempt, meaning the other half either miss the pattern or hit edge cases. If this lands in your live assessment and you freeze, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Populating Next Right Pointers in Each Node II"
Populating Next Right Pointers in Each Node II 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. Built by an Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe naive approach uses a queue to level-order traverse and connect nodes, which works but costs extra space. The real trick is doing it with O(1) space by using the next pointers you've already populated in the previous level as your traversal guide. You build the next level's connections while walking the current level via pointers, not a queue. The gap is that with a non-perfect tree, you can't assume every node has both children, so you need to skip nulls and find the actual next node to process. Most errors come from forgetting to handle disconnected subtrees or reusing a current pointer incorrectly. Breadth-First Search and Depth-First Search both appear in the topic tags because either approach can work, but the constant-space BFS variant is the interviewer's ideal answer. StealthCoder hedges the moment you realize the queue-based solution isn't good enough and you need to rebuild your logic live.
Pattern tags
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Make sure you actually pass it.
Populating Next Right Pointers in Each Node II 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. Built by an Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Populating Next Right Pointers in Each Node II interview FAQ
Is Populating Next Right Pointers still asked at big tech?+
Yes. It appears in reports from Snowflake, Citadel, and Walmart Labs. With 55% acceptance, it's a middle-tier gatekeeper. Most likely if you're doing a tree round, not guaranteed, but common enough to drill.
What's the trick I'm missing if the queue solution feels too easy?+
The interviewer wants O(1) space. Once you realize the tree isn't perfect and you can't use math, the insight is using the next pointers from the previous level as your iteration backbone. That's what separates AC from TLE or memory limit exceeded.
How does this relate to the other 'Next Right Pointer' problem?+
The first version assumes a perfect binary tree, so a formula works. This one drops that guarantee. Both test level-order traversal, but this version forces you to think about in-place connection. It's the harder variant.
Do I need DFS or BFS?+
BFS is more intuitive for level-order, but the optimal constant-space solution mimics BFS using next pointers, not a queue. DFS works too if you're disciplined, but most solutions lean BFS-style thinking.
What are the most common failures on this problem?+
Forgetting to handle null children, losing your place while iterating the current level, or not resetting pointers between levels. Edge cases with single-child nodes or incomplete levels trip up about half the attempts.
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