Bit Manipulation - Single Number II (Three Copies)
Identify the bug in the following code snippet for Single Number II using the bitwise FSM approach:
Identify the bug in the following code snippet for Single Number II using the bitwise FSM approach:
medium🐞 Bug Identification Q14 of Q15
Step-by-Step Solution
Step 1: Compare common_mask calculation with correct formula
The correct mask is the negation of the AND of ones and twos, i.e., ~(ones & twos), not ~(ones | twos).Step 2: Understand impact of wrong mask
Using OR instead of AND causes bits to be cleared incorrectly, failing to reset bits appearing thrice properly.Final Answer:
Option C -> Option CQuick Check:
Correct mask uses AND, not OR, to clear bits appearing three times [OK]
Quick Trick: Mask must clear bits appearing in both ones and twos simultaneously [OK]
Common Mistakes:
MISTAKES- Using OR instead of AND in mask
- Misordering bit updates
Trap Explanation:
PITFALL- OR looks similar and plausible but breaks the FSM logic subtly.
Interviewer Note:
CONTEXT- Tests candidate's attention to subtle bitwise logic details
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