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What is the time complexity of the bottom-up subset sum dynamic programming algorithm given n items and target sum S?

medium🪤 Complexity Trap Q5 of Q15
Dynamic Programming: Knapsack - Subset Sum
What is the time complexity of the bottom-up subset sum dynamic programming algorithm given n items and target sum S?
AO(n + S)
BO(S^n)
CO(n^2)
DO(n * S)
Step-by-Step Solution
Solution:
  1. Step 1: Analyze nested loops

    Outer loop runs n times; inner loop runs up to S times.
  2. Step 2: Multiply loops for total complexity

    Total time is O(n * S) due to nested iteration over items and sums.
  3. Final Answer:

    Option D -> Option D
  4. Quick Check:

    DP table size is n by S [OK]
Quick Trick: Nested loops over n and S -> O(n * S) [OK]
Common Mistakes:
MISTAKES
  • Confusing with O(n + S)
  • Assuming exponential due to subsets
Trap Explanation:
PITFALL
  • Candidates often forget S factor or confuse with brute force exponential time.
Interviewer Note:
CONTEXT
  • Tests understanding of DP time complexity and nested loops.
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