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Train Schedule Reachability
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Train Schedule Reachability

MediumPython

Problem

Glean may need to determine whether a user can travel between offices using a fixed train schedule. Given a starting station, destination, earliest departure time, and train trips, return whether the destination is reachable through zero or more connections.

Each trip is represented as [from_station, to_station, departure_time, arrival_time]. A passenger can board a trip only if they are already at from_station and departure_time >= their arrival time at that station. Times are integer minutes from the start of the day, and every trip arrives no earlier than it departs.

Formal Specification

Implement can_reach(start, destination, start_time, trips), where start and destination are strings, start_time is an integer, and trips is a list of four-element lists. Return a boolean. The passenger is considered to have reached the destination immediately when start == destination.

Constraints

  • 1 <= len(trips) <= 10^5
  • Station names are non-empty strings
  • 0 <= start_time, departure_time, arrival_time <= 10^9
  • departure_time <= arrival_time for every trip
  • A passenger may wait at a station between trains

Function Signature

def can_reach(start, destination, start_time, trips):
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