0

If the input array can contain negative numbers and the bit counting approach is used, what modification is necessary to correctly find the single number?

hard🎤 Interviewer Follow-up Q15 of Q15

Bit Manipulation - Single Number II (Three Copies)

If the input array can contain negative numbers and the bit counting approach is used, what modification is necessary to correctly find the single number?

AUse a 32-bit mask and handle sign bit separately to avoid sign extension errors.

BUse a hash map instead, as bit counting cannot handle negatives.

CConvert all numbers to positive before bit counting and restore sign later.

DNo modification needed; bit counting works the same for negatives.

Step-by-Step Solution

Step 1: Understand bit counting with negative numbers
Negative numbers use two's complement; sign bit must be handled carefully to avoid incorrect counts.
Step 2: Apply 32-bit mask and handle sign bit
Counting bits with a mask ensures correct accumulation; sign bit handled separately prevents sign extension issues.
Final Answer:
Option A -> Option A
Quick Check:
Proper masking ensures correct bit counts for negatives [OK]

Quick Trick: Mask bits to handle sign bit correctly in negative numbers [OK]

Common Mistakes:

MISTAKES

Ignoring sign bit causes wrong results
Assuming negatives behave like positives

Trap Explanation:

PITFALL

Neglecting sign bit handling looks like bit counting but yields wrong answers.

Interviewer Note:

CONTEXT

Checks depth of understanding for bitwise solutions with signed integers

Master "Single Number II (Three Copies)" in Bit Manipulation

3 interactive learning modes - each teaches the same concept differently

Try It Solution Trace

Want More Practice?

15+ quiz questions · All difficulty levels · Free

Free Signup - Practice All Questions

More Bit Manipulation Quizzes