Discussion on: Minimum Number of Platforms Required for a Railway Station, Bloomberg Interview question. 🚄🚄🚄

[Aleksander Maj]

I always appreciate interesting coding challenges during the interview, here is my solution using some light functional methods:

const arr = [900, 940, 950, 1100, 1500, 1800];
const dept = [910, 1200, 1120, 1130, 1900, 2000];

const numPlatforms = (arrivals, departures) => (
  [
  ...arrivals.map(time => ({time, value: 1})), 
  ...departures.map(time => ({time, value: -1}))
  ].
  sort((a,b) => (a.time - b.time)).
  reduce((acc, s) => ({
    value: (acc.value + s.value),
    max: Math.max(acc.max, acc.value)
  }), {value: 0, max: 0}).
  max
);

numPlatforms(arr, dept);

[Akhil]

Hi ! thanks for your solution. Could you explain the flow of execution? I am not that well versed in javascript methods.

[Aleksander Maj]

1. It merges an array of arrivals with departures and adds some values (1 when the train arrives and -1 when it departures). Result of it should be an array of sth like:
   [{time: 9:00, value: 1}, ....,{time: 2000, value: -1}]

2. Then I sort it like you did it.

3. .reduce is loop that's going through the "timetable" and it is doing two things:

   • add 1 if train comes and subtracts if it departures
   • check what is current number of trains and save max of this value

[Akhil]

Wow! This is so efficient! Thanks for sharing it !!