Suppose the problem is changed so that candidates can be reused unlimited times (unlike original no reuse). Which modification to the backtracking algorithm correctly adapts to this change?
hard🎤 Interviewer Follow-up Q15 of Q15
Subsets & Combinations - Combination Sum II (No Reuse, Duplicates)
Suppose the problem is changed so that candidates can be reused unlimited times (unlike original no reuse). Which modification to the backtracking algorithm correctly adapts to this change?
AChange recursive call from backtrack(i + 1, ...) to backtrack(i, ...) to allow reuse of the same candidate
BKeep backtrack(i + 1, ...) but remove duplicate skipping to allow repeated combinations
CAdd a global visited set to prevent reusing candidates in the same combination
DSort candidates and prune only when candidate >= target, but keep recursion unchanged
Step-by-Step Solution
Step 1: Understand reuse requirement
Allowing reuse means the same candidate index can be chosen multiple times in the same combination.
Step 2: Modify recursion call
Changing recursive call from backtrack(i + 1, ...) to backtrack(i, ...) allows the same candidate to be reused multiple times.
Step 3: Keep duplicate skipping and pruning as before
Duplicate skipping still applies to avoid repeated combinations, and pruning remains to optimize.
Final Answer:
Option A -> Option A
Quick Check:
Recurse with same index to allow reuse [OK]
Quick Trick:Reuse means recurse with same index, not next index [OK]
Common Mistakes:
MISTAKES
Removing duplicate skipping causes duplicates
Using visited set breaks reuse logic
Pruning incorrectly changes conditions
Trap Explanation:
PITFALL
Removing duplicate skipping or using visited sets breaks uniqueness or reuse logic.
Interviewer Note:
CONTEXT
Tests if candidate can adapt backtracking for reuse variants correctly.
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