Subsets & Combinations - Combination Sum III (K Numbers to N)
Suppose the problem is changed so that numbers 1 to 9 can be used unlimited times to form combinations of size k summing to n. Which approach is best suited to solve this variant?
Suppose the problem is changed so that numbers 1 to 9 can be used unlimited times to form combinations of size k summing to n. Which approach is best suited to solve this variant?
hard🎤 Interviewer Follow-up Q10 of Q15
Step-by-Step Solution
Solution:
Step 1: Understand problem change
Numbers can be reused unlimited times; size k fixed; sum n.Step 2: Identify suitable approach
Backtracking with start index unchanged allows reuse of same number multiple times.Step 3: Compare with other approaches
Sum bound pruning needs adjustment; DP possible but backtracking with repeats is straightforward.Final Answer:
Option A -> Option AQuick Check:
Allow repeats by not incrementing start index [OK]
Quick Trick: Allow repeats -> do not increment start index in backtracking [OK]
Common Mistakes:
MISTAKES- Using original code without change
- Trying greedy or DP unnecessarily
Trap Explanation:
PITFALL- Candidates often forget to adjust start index to allow repeats, breaking correctness.
Interviewer Note:
CONTEXT- Tests ability to adapt backtracking to problem variants with repeats.
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