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Which modification to the algorithm correctly computes the minimum cost to connect all sticks under this new rule?

hard🎤 Interviewer Follow-up Q15 of Q15
Greedy Algorithms - Minimum Cost to Connect Sticks
Suppose now you can reuse sticks after merging (i.e., merged sticks remain available for future merges without removal). Which modification to the algorithm correctly computes the minimum cost to connect all sticks under this new rule?
AUse a dynamic programming approach to consider all merge sequences
BSort sticks once and merge sticks in ascending order without a heap
CThe problem becomes ill-defined; no algorithm can guarantee minimum cost with reuse
DUse the same min-heap approach but do not remove merged sticks from the heap
Step-by-Step Solution
Solution:
  1. Step 1: Understand reuse impact

    If sticks can be reused infinitely, merges do not reduce the number of sticks, so the problem changes fundamentally.
  2. Step 2: Analyze problem feasibility

    Because sticks remain after merging, the process can continue indefinitely, making minimum total cost undefined or infinite.
  3. Final Answer:

    Option C -> Option C
  4. Quick Check:

    Reuse breaks the problem constraints -> no minimal cost solution [OK]
Quick Trick: Reusing sticks breaks problem constraints -> no minimal cost [OK]
Common Mistakes:
MISTAKES
  • Assuming min-heap still works without removing merged sticks
  • Trying to sort once ignoring dynamic merges
  • Attempting DP without problem redefinition
Trap Explanation:
PITFALL
  • Candidates may think reuse is a minor change, but it fundamentally breaks the problem's termination and minimality.
Interviewer Note:
CONTEXT
  • Tests candidate's ability to reason about problem constraints and algorithm applicability under variants.
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