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Given a set of train schedules with arrival and departure times, which technique efficiently calculates the minimum number of platforms required to avoid any waiting?

easy💻 Programming Q1 of Q15
Intervals - Minimum Number of Platforms Required
Given a set of train schedules with arrival and departure times, which technique efficiently calculates the minimum number of platforms required to avoid any waiting?
AGreedy selection of earliest finishing trains only
BDynamic programming with memoization
CDepth-first search on a graph representation
DSorting events and using a two-pointer sweep line approach
Step-by-Step Solution
Solution:

  1. Step 1: Sort arrival and departure times separately

    Sorting allows sequential processing of events in chronological order.

  2. Step 2: Use two pointers to traverse arrivals and departures

    Increment platform count on arrival, decrement on departure.

  3. Final Answer:

    Option D -> Option D

  4. Quick Check:

    Sorting + two pointers efficiently track overlaps [OK]
Quick Trick: Sort arrivals and departures, then sweep with two pointers [OK]
Common Mistakes:
MISTAKES
  • Assuming dynamic programming is needed for interval overlaps
  • Using graph traversal which is unnecessary here
  • Greedy approach ignoring overlapping intervals
Trap Explanation:
PITFALL
  • Other options seem plausible but don't handle interval overlaps efficiently.
Interviewer Note:
CONTEXT
  • Tests understanding of the core algorithmic pattern for interval overlap problems.
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