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What is the space complexity of the memoized recursive job scheduling solution that caches results for each job index?

medium🪤 Complexity Trap Q6 of Q15
Dynamic Programming: Knapsack - Maximum Profit in Job Scheduling
What is the space complexity of the memoized recursive job scheduling solution that caches results for each job index?
AO(1)
BO(n^2)
CO(n) including recursion stack and memo
DO(n log n)
Step-by-Step Solution
Solution:
  1. Step 1: Memo dictionary stores results for each job index

    Memo size is O(n).
  2. Step 2: Recursion stack depth is O(log n) due to binary search

    Each recursive call reduces problem size via binary search, so max stack depth is O(log n).
  3. Step 3: Total space is memo + recursion stack = O(n + log n) ≈ O(n)

    But binary search arrays and sorting add O(n log n) auxiliary space in some implementations.
  4. Final Answer:

    Option D -> Option D
  5. Quick Check:

    Memo + recursion stack + sorting -> O(n log n) [OK]
Quick Trick: Memo + recursion stack + sorting -> O(n log n) [OK]
Common Mistakes:
MISTAKES
  • Ignoring recursion stack space
  • Assuming constant space for memo
Trap Explanation:
PITFALL
  • Candidates often forget recursion stack or auxiliary arrays in space calculation.
Interviewer Note:
CONTEXT
  • Tests understanding of space usage in recursive DP with memoization.
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