Tree traversals (inorder, preorder, postorder) in Data Structures Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the traversal order

Given a binary tree, which traversal visits the root node first, then the left subtree, and finally the right subtree?

A Level-order traversal

B Inorder traversal

C Postorder traversal

D Preorder traversal

💡 Hint

Think about which traversal starts by visiting the root node before its children.

Preorder traversal visits the root node first, then recursively visits the left subtree, followed by the right subtree.

📋 Factual

intermediate

Output of inorder traversal

What is the output sequence of an inorder traversal on the following binary tree?

2
/ \
1 3

A [2, 1, 3]

B [1, 2, 3]

C [3, 2, 1]

D [1, 3, 2]

💡 Hint

Inorder traversal visits left subtree, root, then right subtree.

Inorder traversal visits nodes in ascending order for a binary search tree: left child (1), root (2), right child (3).

🔍 Analysis

advanced

Determine postorder traversal output

Consider this binary tree:

A
/ \
B C
/ / \
D E F

What is the postorder traversal output?

A [B, D, A, E, F, C]

B [A, B, D, C, E, F]

C [D, B, E, F, C, A]

D [D, B, C, E, F, A]

💡 Hint

Postorder traversal visits left subtree, right subtree, then root.

Postorder visits D (leftmost), then B, then E and F (right subtree), then C, and finally root A.

❓ Comparison

advanced

Compare preorder and postorder traversals

Which statement correctly compares preorder and postorder traversals of a binary tree?

A Preorder visits the root before its subtrees; postorder visits the root after its subtrees.

B Preorder visits the root after its subtrees; postorder visits the root before its subtrees.

C Both preorder and postorder visit the root at the same time.

D Preorder and postorder always produce the same node sequence.

💡 Hint

Think about when the root node is visited in each traversal.

Preorder traversal visits the root node first, while postorder traversal visits it last after its children.

❓ Reasoning

expert

Number of nodes visited in preorder traversal

A binary tree has 7 nodes. How many nodes will be visited during a complete preorder traversal?

A 7

B 6

C 8

D Depends on the tree structure

💡 Hint

Traversal visits every node exactly once.

Preorder traversal visits every node in the tree exactly once, so all 7 nodes are visited.