Tree problems,
and the tell.
The structure is a hierarchy and the answer is about a node, a path, or a subtree. 135 problems in the catalogue carry this tag, from first-week easy to interview hard.
Free to start. Running and submitting a solution never costs credits.
How the pattern actually works.
One mechanism, and the mistake that costs people the problem.
The tell. The structure is a hierarchy and the answer is about a node, a path, or a subtree.
The mechanism. Every node is the root of a smaller problem, so recursion fits: solve the children, then combine. The order you handle the node in, before or after the children, is the whole difference.
What goes wrong. Forgetting the empty tree. A null node is a real case, not an error.
The ones asked most often.
By how often the catalogue records them being set, not by our opinion.
- Binary Tree CamerasHardasked at 8 companies
- Create Binary Tree From DescriptionsMediumasked at 2 companies
- Difference Between Maximum and Minimum Price SumHardasked at 2 companies
- Maximum XOR of Two Non-Overlapping SubtreesHardasked at 2 companies
- Count Nodes Equal to Average of SubtreeMediumasked at 2 companies
- Path Sum IVMediumasked at 1 companies
- Cycle Length Queries in a TreeHardasked at 1 companies
- Maximize Sum of Weights after Edge RemovalsHardasked at 1 companies
- Minimum Number of Operations to Sort a Binary Tree by LevelMediumasked at 1 companies
- Binary Tree PruningMediumasked at 1 companies
Read it, watch it, then solve it.
The order that makes a pattern stick.
Everything in the app, in one place.
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Problems filed under the pattern that solves them, not a sheet.
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About tree problems.
Free to start, no card.
Start practisingHow do I know a problem is a tree problem?
The structure is a hierarchy and the answer is about a node, a path, or a subtree.
How many tree problems should I solve?
Enough to stop needing the hint, which is usually ten to fifteen across the levels, not the whole list. The catalogue tags 135, split roughly 27 easy, 83 medium and 25 hard in the sample we show, so work up rather than across.
What goes wrong most often in tree problems?
Forgetting the empty tree. A null node is a real case, not an error.
Is practising by pattern better than a problem sheet?
A sheet tells you what to solve. A pattern tells you why those problems sit together, which is the part that carries over to the problem you have not seen. That is why the app files every problem under its pattern.