Tree Node
A medium-tier problem at 74% community acceptance, tagged with Database. Reported in interviews at X and 0 others.
Tree Node is a database problem that tests your ability to classify hierarchical relationships in SQL. With a 74% acceptance rate, it looks straightforward until you hit the filtering logic. The catch: you need to identify root, leaf, and inner nodes in a single query without overthinking it. This problem appears rarely but when it does, candidates either nail it fast or spend 20 minutes debugging their case logic. If it shows up in your OA and you blank on the node classification pattern, StealthCoder runs invisibly and surfaces the working query in seconds.
Companies that ask "Tree Node"
Tree Node 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick here is recognizing that node classification requires a self-join to check parent-child relationships. A root node has no parent, a leaf node has no children, and everything else is an inner node. Most candidates start with three separate queries or nested case statements that quickly become unreadable. The real pattern is a single case statement leveraging a left join or exists check to determine each node's type. Common pitfall: forgetting to handle the case where the parent column points to itself or null inconsistently. The database syntax varies slightly across SQL dialects, which is why the pattern matters more than memorizing the exact syntax. StealthCoder handles the dialect variation and delivers the exact query for your platform.
Pattern tags
You know the problem.
Make sure you actually pass it.
Tree Node 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 for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Tree Node interview FAQ
Is Tree Node actually asked at interviews?+
Rarely. It's a single-company report in the data, which means low frequency in the wild. But it's the exact problem type that shows up without warning in medium-difficulty OA rounds. Worth knowing the pattern, not memorizing.
What's the main trick I'm missing if I get stuck?+
Self-join. Most people try to solve it with subqueries. The efficient move is one case statement with a left join back to the same table to check if a parent exists (root), or check if children exist (leaf).
How hard is a 74% acceptance rate for a medium problem?+
That's above average for medium. It means the problem is more pattern-recognition than algorithmic puzzle. Once you see the self-join trick, it's straightforward. Most failures are sloppy case logic or SQL syntax errors.
Will I need to know tree algorithms for this?+
No. This is pure SQL, not algorithms. You're classifying nodes based on their relationships in the table, not traversing or searching. Understanding parent-child relationships in a relational model is all you need.
Does the SQL dialect matter here?+
Yes. NULL handling, join syntax, and case statement ordering differ between MySQL, PostgreSQL, and SQL Server. The pattern is universal, but the exact query varies. StealthCoder handles your specific platform.
Want the actual problem statement? View "Tree Node" on LeetCode →