Which modification to the iterative approach correctly generates all unique subsets with duplicates and unlimited reuse?
hard🎤 Interviewer Follow-up Q15 of Q15
Subsets & Combinations - Subsets II (With Duplicates)
Suppose the problem changes: now each element in the input array can be chosen multiple times (unlimited reuse), and duplicates still exist. Which modification to the iterative approach correctly generates all unique subsets with duplicates and unlimited reuse?
AKeep the same code but remove the duplicate skipping condition to allow reuse.
BSort the array, and for each element, always start from index 0 when adding new subsets to allow reuse, but skip duplicates at the same recursion level.
CSort the array, and for each element, start from the previous start index for duplicates, but allow reuse by appending to all existing subsets including newly added ones in the same iteration.
DUse backtracking with a visited array to track reuse and skip duplicates by sorting.
Step-by-Step Solution
Solution:
Step 1: Understand unlimited reuse impact
Unlimited reuse means subsets can include the same element multiple times, so the iteration must consider all existing subsets each time.
Step 2: Modify iteration start index
To allow reuse, always start from index 0 when adding new subsets, so elements can be appended multiple times. However, duplicates must still be skipped at the same recursion level to avoid repeated subsets.
Step 3: Confirm skipping duplicates at recursion level
Skipping duplicates at the same recursion level prevents generating identical subsets multiple times despite reuse.
Final Answer:
Option B -> Option B
Quick Check:
Starting from 0 allows reuse; skipping duplicates avoids repeats [OK]
Quick Trick:Start from 0 to allow reuse; skip duplicates at recursion level [OK]
Common Mistakes:
MISTAKES
Removing duplicate skipping causes duplicates
Starting from previous start index blocks reuse
Using visited array unnecessarily complicates iterative approach
Trap Explanation:
PITFALL
Removing duplicate skipping looks simpler but causes duplicates; starting from previous start index blocks reuse.
Interviewer Note:
CONTEXT
Tests candidate's ability to adapt subset generation to reuse constraints and maintain uniqueness.
Master "Subsets II (With Duplicates)" in Subsets & Combinations
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