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What is the space complexity of the top-down memoized 0/1 Knapsack solution with n items and capacity W?

medium🪤 Complexity Trap Q6 of Q15
Dynamic Programming: Knapsack - 0/1 Knapsack Problem
What is the space complexity of the top-down memoized 0/1 Knapsack solution with n items and capacity W?
AO(n)
BO(n * W + n) due to recursion stack and memo
CO(n * W)
DO(W)
Step-by-Step Solution
Solution:
  1. Step 1: Memoization table size

    Memo stores results for each (i, w) pair -> O(n * W) space.
  2. Step 2: Recursion stack depth

    Maximum recursion depth is n, adding O(n) auxiliary space.
  3. Step 3: Total space

    Sum of memo and recursion stack -> O(n * W + n).
  4. Final Answer:

    Option B -> Option B
  5. Quick Check:

    Memo + recursion stack space combined -> O(n*W + n) [OK]
Quick Trick: Memo table plus recursion stack -> O(n*W + n)
Common Mistakes:
MISTAKES
  • Ignoring recursion stack space
  • Assuming only memo space counts
Trap Explanation:
PITFALL
  • Candidates forget recursion stack adds to total space complexity.
Interviewer Note:
CONTEXT
  • Tests understanding of auxiliary space in recursive DP
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