Bit Manipulation - Single Number (XOR Self-Cancellation)
The following code attempts to find the single number in an array using XOR. Identify the line containing the subtle bug that causes incorrect results.
The following code attempts to find the single number in an array using XOR. Identify the line containing the subtle bug that causes incorrect results.
medium🐞 Bug Identification Q14 of Q15
Step-by-Step Solution
Step 1: Analyze initialization of result
Result initialized to nums[0], then XORed again with nums[0] in loop, cancelling it out incorrectly.Step 2: Understand correct initialization
Result should start at 0 so XOR accumulates all elements exactly once.Final Answer:
Option A -> Option AQuick Check:
Initializing to zero avoids double XOR of first element [OK]
Quick Trick: XOR accumulator must start at zero [OK]
Common Mistakes:
MISTAKES- Initializing with first element causes double XOR
- Loop includes first element again
- Misplaced return statement
Trap Explanation:
PITFALL- Starting with first element looks plausible but causes double cancellation of that element.
Interviewer Note:
CONTEXT- Checks if candidate spots subtle initialization bugs that break XOR logic.
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