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Consider the following buggy code snippet for building a tree from inorder and postorder traversals. Which line contains the subtle bug that can cause incorrect tree construction or runtime errors?

medium🐞 Bug Identification Q14 of Q15

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

Consider the following buggy code snippet for building a tree from inorder and postorder traversals. Which line contains the subtle bug that can cause incorrect tree construction or runtime errors?

ALine creating root node with postorder[-1]

BLine initializing inorder_index to 0

CLine attaching node as right child

DLine popping from stack inside while loop

Step-by-Step Solution

Step 1: Identify inorder_index initialization
inorder_index should start at the last index (len(inorder) - 1) because postorder is processed from end to start.
Step 2: Consequences of wrong initialization
Starting at 0 causes incorrect comparisons and popping logic, leading to wrong tree structure or runtime errors.
Final Answer:
Option B -> Option B
Quick Check:
Correct inorder_index initialization is critical for stack popping logic [OK]

Quick Trick: inorder_index must start at last index, not zero [OK]

Common Mistakes:

MISTAKES

Wrong inorder_index initialization
Confusing postorder traversal direction
Incorrect stack popping conditions

Trap Explanation:

PITFALL

This subtle off-by-one initialization bug passes many tests but breaks on larger inputs.

Interviewer Note:

CONTEXT

Tests if candidate can spot subtle index initialization bugs that cause logical errors.

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