Given the following optimized recursive code snippet for building a tree from inorder and postorder traversals, what is the value of the root node constructed for inorder = [9,3,15,20,7] and postorder = [9,15,7,20,3]?

easy🧾 Code Trace Q3 of Q15

Tree: Depth-First Search - Construct Tree from Inorder and Postorder

A20

B15

Step-by-Step Solution

Solution:

Step 1: Identify root from postorder last element
postorder[-1] = 3, so root node value is 3.
Step 2: Confirm root value matches expected tree root
3 is the root splitting inorder into left [9] and right [15,20,7].
Final Answer:
Option D -> Option D
Quick Check:
Root is last postorder element 3 [OK]

Quick Trick: Root is last element in postorder traversal [OK]

Common Mistakes:

MISTAKES

Picking first element of inorder or postorder
Mixing up traversal roles

Trap Explanation:

PITFALL

Candidates often confuse root position in traversals, picking wrong root value.

Interviewer Note:

CONTEXT

Tests ability to trace recursive tree construction on canonical input.

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More Tree: Depth-First Search Quizzes

Given the following optimized recursive code snippet for building a tree from inorder and postorder traversals, what is the value of the root node constructed for inorder = [9,3,15,20,7] and postorder = [9,15,7,20,3]?

Step 1: Identify root from postorder last element

Step 2: Confirm root value matches expected tree root

Final Answer:

Quick Check:

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