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The following code attempts to find the missing number using XOR. Which line contains the subtle bug that causes incorrect results when the missing number is n?

medium🐞 Bug Identification Q14 of Q15

Bit Manipulation - Find the Missing Number

The following code attempts to find the missing number using XOR. Which line contains the subtle bug that causes incorrect results when the missing number is n?

ALine 3: initializing xor_all to 0

BLine 7: returning xor_all without modification

CLine 4: iterating only to n-1 instead of n

DLine 6: XORing array elements

Step-by-Step Solution

Step 1: Analyze the loop range for XORing indices
The loop runs from 0 to n-1 (range(n)), missing the number n itself.
Step 2: Understand impact on missing number detection
Since n is not XORed, if n is the missing number, it won't be accounted for, causing wrong output.
Final Answer:
Option C -> Option C
Quick Check:
Changing loop to range(n+1) fixes the bug [OK]

Quick Trick: Loop must include n to XOR all indices correctly [OK]

Common Mistakes:

MISTAKES

Off-by-one in loop range
Forgetting to XOR n
Assuming initialization causes bug

Trap Explanation:

PITFALL

Range(n) looks correct but excludes n, a subtle off-by-one error common in indexing problems.

Interviewer Note:

CONTEXT

Tests candidate's attention to boundary conditions and off-by-one errors in bit manipulation

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