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What is the space complexity of the top-down memoization approach for the minimum subset sum difference problem with n elements and total sum W?

medium🪤 Complexity Trap Q6 of Q15
Dynamic Programming: Knapsack - Minimum Subset Sum Difference
What is the space complexity of the top-down memoization approach for the minimum subset sum difference problem with n elements and total sum W?
AO(W)
BO(n + W)
CO(n * W)
DO(n)
Step-by-Step Solution
Solution:
  1. Step 1: Analyze memo storage

    Memo stores results for states (i, curr_sum), total O(n * W) entries.
  2. Step 2: Consider recursion stack

    Recursion depth is O(n), so stack space O(n).
  3. Step 3: Total space complexity

    Memo + recursion stack = O(n * W) + O(n) ≈ O(n * W), but since W dominates, space is O(n * W).
  4. Final Answer:

    Option B -> Option B
  5. Quick Check:

    Memo table plus recursion stack -> O(n + W) is minimal, but actual is O(n * W) [OK]
Quick Trick: Memo table size x recursion depth -> O(n * W) space [OK]
Common Mistakes:
MISTAKES
  • Ignoring recursion stack or memo size
Trap Explanation:
PITFALL
  • Candidates pick O(W) or O(n) ignoring combined memo and stack space.
Interviewer Note:
CONTEXT
  • Tests understanding of auxiliary space in recursive DP.
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