The station platforms

Problem

At Highvale station no train ever waits: a platform is always free when it pulls in. From today's timetable, the stationmaster opens just enough. Write a function that takes arrivals and departures, two lists of integers of the same length (minutes of the day, from 0 to 1439; they may be empty). Train i arrives at arrivals[i] and leaves at departures[i], always at least one minute after arriving. Return an integer: the most trains that are in the station at the same time.

A train holds its platform from the minute it arrives until it leaves, and on the minute it leaves the platform is already free: if another train arrives that same minute, it can use it.

With arrivals [10, 15, 40, 45] and departures [30, 50, 60, 55], at minute 45 the last three are in (the first left at 30): the answer is 3. With no trains, the answer is 0.

Examples

• The one from the example

  [10, 15, 40, 45], [30, 50, 60, 55] → 3

• They never overlap

  [0, 20, 40], [10, 30, 50] → 1

• One leaves the minute another arrives

  [60, 120], [120, 180] → 1

• The timetable comes out of order

  [300, 100, 200], [400, 350, 250] → 2

• No trains

  [], [] → 0

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def peak(arrivals, departures):
    pass

function peak(arrivals, departures) {
}