Subsets & Combinations - Subsets II (With Duplicates)
Consider the following Python code for generating subsets with duplicates. What is the value of
res after processing the input [1, 2, 2]?Consider the following Python code for generating subsets with duplicates. What is the value of res after processing the input [1, 2, 2]?
easy🧾 Code Trace Q12 of Q15
Step-by-Step Solution
Solution:
Step 1: Trace iterations for input [1, 2, 2]
Start with res = [[]]. - i=0 (num=1): s=0, start=1, add [1] -> res = [[], [1]] - i=1 (num=2): s=0, start=2, add [2], [1,2] -> res = [[], [1], [2], [1,2]] - i=2 (num=2): duplicate, s=start from previous iteration=2, start=4, add [2,2], [1,2,2] -> res = [[], [1], [2], [1,2], [2,2], [1,2,2]]Step 2: Confirm final res matches option
The final res contains exactly these subsets without duplicates: [], [1], [2], [1,2], [2,2], [1,2,2].Final Answer:
Option A -> Option AQuick Check:
Output matches expected unique subsets for input [1,2,2] [OK]
Quick Trick: Duplicate skips start index to avoid repeats [OK]
Common Mistakes:
MISTAKES- Appending duplicates multiple times by resetting s=0 always
- Off-by-one errors in start index
- Including extra subsets from previous iterations
Trap Explanation:
PITFALL- Confusing when to reset start index causes duplicates or missing subsets.
Interviewer Note:
CONTEXT- Tests ability to mentally execute backtracking with duplicate skipping.
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