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Which approach correctly adapts the solution?

hard🎤 Interviewer Follow-up Q15 of Q15
Greedy Algorithms - Two City Scheduling
Suppose the problem is changed so that some people can be assigned to either city multiple times (reusable assignments), or the number of people sent to each city is not fixed. Which approach correctly adapts the solution?
AUse a dynamic programming approach to handle variable counts and reuse assignments
BUse the same greedy sorting by cost difference and assign exactly n people to each city
CSort by absolute cost to city A and assign all to city A to minimize cost
DAssign people greedily without sorting, picking the cheaper city for each person
Step-by-Step Solution
Solution:
  1. Step 1: Understand problem change

    Allowing reuse or variable counts breaks the fixed half assignment constraint, invalidating the greedy approach.
  2. Step 2: Why DP is needed

    Dynamic programming can explore all valid assignments with reuse or variable counts, ensuring minimal total cost under new constraints.
  3. Final Answer:

    Option A -> Option A
  4. Quick Check:

    Greedy fails when constraints are relaxed; DP handles complex state space [OK]
Quick Trick: Relaxed constraints require DP, not greedy [OK]
Common Mistakes:
MISTAKES
  • Applying greedy unchanged despite constraint changes
  • Ignoring reuse possibility in assignment
  • Assuming sorting by absolute cost suffices
Trap Explanation:
PITFALL
  • Greedy looks simpler but fails when assignment constraints are relaxed or reuse allowed.
Interviewer Note:
CONTEXT
  • Evaluates candidate's ability to adapt solutions to constraint changes and recognize greedy limitations.
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