Intermediate~2h
Trees: DFS & Recursion in Data Structures & AlgorithmsInterview Readiness Check
Recursive tree traversal — path sum, LCA, diameter, max depth, serialize/deserialize.
inorderpreorderpostorderLCApath sumdiameterDFS stack
Learning path
Trees: BFS & Level Order→Trees: DFS & Recursion ← you are here→Tries & Prefix TreesBacktrackingGraph Algorithms
Try a sample question
Validate a Binary Search Tree. Consider this tree: root=5, root.left=3, root.left.right=6. A student writes `return node.left.val < node.val < node.right.val` for each node. The tree passes their check. What is wrong?
A.The check works for this tree; the real bug is not handling null children
B.Recursion never terminates for BSTs with duplicate values — the check should use ≤ instead of <
C.The check only looks at immediate children. Node 3 has right child 6, which satisfies 6 > 3 locally, but 6 sits in 5's left subtree and violates 6 < 5 globally. The validator must propagate an allowed range down the tree, or perform an in-order traversal and confirm strictly increasing order.
D.BST validation requires level-order traversal because DFS visits nodes in the wrong order
Sign up free to take the full check and see the answer with an explanation.
What this module tests
- Conceptual understanding of trees: dfs & recursion fundamentals
- Trade-offs and design decisions in real system scenarios
- inorder and preorder — applied knowledge
- Interview-style reasoning and explanation quality
Free to start
Take the Trees: DFS & Recursion check →
10 questions · Dimension scoring · AI coach feedback · Shareable result
Test your knowledge — free →No credit card · Takes 10–15 min
Frequently asked questions
- What does the Trees: DFS & Recursion check test?
- The check covers recursive tree traversal — path sum, lca, diameter, max depth, serialize/deserialize. Questions span beginner to advanced difficulty and test both conceptual understanding and practical trade-off reasoning.
- What keywords should I know for Trees: DFS & Recursion?
- Key concepts include: inorder, preorder, postorder, LCA, path sum, diameter, DFS stack. These frequently appear in data structures & algorithms interviews at product and infrastructure companies.
- How many questions are in the check?
- Each check has 10 questions — a mix of MCQ and short-answer. You get scored by dimension (e.g., scalability, consistency) so you know exactly where to focus.
- How long does it take to study Trees: DFS & Recursion?
- Most engineers spend around 2 hours on this module. The check itself takes about 10–15 minutes. You can retake it up to 3 times per day.
- What prerequisite knowledge do I need before Trees: DFS & Recursion?
- Trees: DFS & Recursion builds on Trees: BFS & Level Order. Complete those first for the best results.
- Is inorder, preorder, postorder covered?
- Yes. The Trees: DFS & Recursion module covers inorder, preorder, postorder among other key concepts. The check includes questions that reflect real data structures & algorithms interview patterns.