Don’t just watch it move
- 1Before stepping, predict the next comparison, pointer move or state update.
- 2Read the explanation and identify the invariant that remains true.
- 3Change the input, then solve the concept quest without guessing.
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Class 9 · DSA · Enrichment
Preorder traversal
Interactive explanation Gamified quiz, feedback & rewards
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DSA enrichment · Learning goals & preparation
By the end, you can…
- Explain Visit order: node → left → right.
- Trace a small input and connect each operation to the algorithm’s rule.
- Explain the implementation’s time and space cost and solve its mission.
Useful preparation: Reading arrays, indexing from zero and following step-by-step instructions. Suggested previous stop: Inorder traversal.
DSA uses suggested Foundation (Class 8), Builder (Class 9) and Advanced (Class 10) levels. It is an enrichment pathway.
Trees · Builder
Preorder traversal
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Step to create the first node.
Ready. Step through the algorithm and explain each change.
traverse(node)if node is empty: returnvisit in order: node → left → rightrecurse on each child exactly once
Preorder traversal quest
Explain the idea, read its complexity, then solve a hands-on or trace mission with your current input.
01 · UnderstandFind the invariant→02 · AnalyseThink about cost→03 · SolveUse the model
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From foundations to advanced patterns
The library covers core DSA techniques with bounded teaching examples. Foundation, Builder and Advanced describe learning progression, rather than a school-class syllabus. Snapshots are stored for playback and are excluded from algorithm-space labels.
Further study: MIT Introduction to Algorithms ↗