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Identify the subtle bug in the following recursive bitmask DP code snippet for generating permutations:

medium🐞 Bug Identification Q7 of Q15
Bit Manipulation - Generate All Permutations Using Bitmask DP
Identify the subtle bug in the following recursive bitmask DP code snippet for generating permutations:
AVariable 'res' is undefined; should assign 'result' to memo
BMissing base case for empty mask
CNot resetting visited bits after recursion
DMemo dictionary is not cleared between calls
Step-by-Step Solution
Solution:

  1. Step 1: Inspect memo assignment

    Code assigns memo[mask] = res, but 'res' is undefined; correct variable is 'result'.

  2. Step 2: Confirm impact

    This causes a NameError or incorrect memoization, breaking recursion caching.

  3. Final Answer:

    Option A -> Option A

  4. Quick Check:

    Correct variable name is critical for memoization [OK]
Quick Trick: Check variable names in memo assignments [OK]
Common Mistakes:
MISTAKES
  • Typos in variable names causing silent bugs
Trap Explanation:
PITFALL
  • Candidates overlook subtle typos in memo assignment lines.
Interviewer Note:
CONTEXT
  • Tests attention to detail and understanding of memoization correctness
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