Bit Manipulation - Single Number (XOR Self-Cancellation)
Identify the subtle bug in the following XOR-based single number code snippet:
def singleNumber(nums):
result = nums[0]
for num in nums:
result ^= num
return result
Identify the subtle bug in the following XOR-based single number code snippet: def singleNumber(nums): result = nums[0] for num in nums: result ^= num return result
medium🐞 Bug Identification Q7 of Q15
Step-by-Step Solution
Solution:
Step 1: Analyze initialization
result starts as nums[0], then XORed again in loop starting at nums[0].Step 2: Effect of double XOR
First element XORed twice cancels out, losing that element's contribution.Final Answer:
Option A -> Option AQuick Check:
Double XOR of first element causes wrong result [OK]
Quick Trick: Initialize result to 0, not first element [OK]
Common Mistakes:
MISTAKES- Starting loop at 0 with non-zero init
- Using addition instead of XOR
Trap Explanation:
PITFALL- Candidates often initialize with first element but still XOR it again, causing cancellation.
Interviewer Note:
CONTEXT- Tests bug spotting in subtle initialization errors.
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