Bit Manipulation - Number of 1 Bits (Hamming Weight)
Suppose the input integer can be negative and you want to count the number of 1 bits in its 32-bit two's complement representation. Which modification ensures correct counting for all integers?
Suppose the input integer can be negative and you want to count the number of 1 bits in its 32-bit two's complement representation. Which modification ensures correct counting for all integers?
hard🎤 Interviewer Follow-up Q15 of Q15
Step-by-Step Solution
Step 1: Understand two's complement representation
Negative numbers have sign-extended bits; masking with 0xFFFFFFFF treats them as unsigned 32-bit values.Step 2: Apply mask before counting bits
Masking ensures right shifts do not propagate sign bit and loop terminates correctly.Final Answer:
Option D -> Option DQuick Check:
Masking with 0xFFFFFFFF handles negative inputs correctly [OK]
Quick Trick: Mask negative inputs to treat as unsigned [OK]
Common Mistakes:
MISTAKES- Using naive loop with signed shifts
- Taking absolute value loses bit pattern
- Left shift does not help counting bits
Trap Explanation:
PITFALL- Taking absolute value seems intuitive but changes bit pattern; naive loop fails on negatives.
Interviewer Note:
CONTEXT- Tests candidate's ability to handle signed integers and bitwise operations correctly.
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