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What is the time complexity of the space-optimized bottom-up dynamic programming solution for the Equal Partition problem, where n is the number of elements and target is half the total sum?

medium🪤 Complexity Trap Q13 of Q15
Dynamic Programming: Knapsack - Equal Partition (Partition Equal Subset Sum)
What is the time complexity of the space-optimized bottom-up dynamic programming solution for the Equal Partition problem, where n is the number of elements and target is half the total sum?
AO(2^n) because the problem explores all subsets in worst case
BO(n * n) because we iterate over all elements and all sums up to n
CO(target^2) because the dp array size is target and we update it multiple times
DO(n * target) because for each element we iterate over sums up to target
Step-by-Step Solution
Solution:
  1. Step 1: Identify loops in the code

    The outer loop runs n times (for each element), and the inner loop runs up to target times (half the total sum).
  2. Step 2: Calculate total time complexity

    Multiplying these gives O(n * target). The dp array updates are constant time per iteration.
  3. Final Answer:

    Option D -> Option D
  4. Quick Check:

    Time depends on number of elements and target sum, not n squared or exponential [OK]
Quick Trick: Time depends on n and target sum, not just n [OK]
Common Mistakes:
MISTAKES
  • Confusing n with target or assuming quadratic in n
  • Forgetting target can be large
Trap Explanation:
PITFALL
  • Option A looks plausible since n appears twice, but inner loop depends on target, not n
Interviewer Note:
CONTEXT
  • Tests understanding of DP complexity and difference between input size and sum constraints
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