Bit Manipulation - Find Two Missing Numbers
Given the following code snippet using XOR partitioning to find two missing numbers, what is the output for n=6 and arr=[1, 2, 4, 6]?
Given the following code snippet using XOR partitioning to find two missing numbers, what is the output for n=6 and arr=[1, 2, 4, 6]?
easy🧾 Code Trace Q3 of Q15
Step-by-Step Solution
Solution:
Step 1: Compute xor_all
XOR 1 to 6 = 1^2^3^4^5^6 = 7; XOR arr = 1^2^4^6 = 7; xor_all = 7 ^ 7 = 0; Actually, let's compute carefully: 1^2=3, 3^3=0, 0^4=4, 4^5=1, 1^6=7; arr XOR: 1^2=3, 3^4=7, 7^6=1; xor_all = 7 ^ 1 = 6.Step 2: Find rightmost set bit and partition
set_bit = 6 & (-6) = 2; Partition numbers and arr by bit 2; XOR partitions yield missing numbers 3 and 5.Final Answer:
Option A -> Option AQuick Check:
Output matches expected missing numbers [OK]
Quick Trick: XOR partitions isolate missing numbers by set bit [OK]
Common Mistakes:
MISTAKES- Incorrect XOR calculation
- Wrong set bit extraction
- Mixing partitions
Trap Explanation:
PITFALL- Candidates often miscalculate xor_all or set_bit, leading to wrong missing numbers.
Interviewer Note:
CONTEXT- Tests candidate's ability to trace XOR partitioning code
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