coding test

consecutive_dates.swift

import Foundation

// Given some sorted dates find out if the set contains 5 dates within 30 days of eachother.
// I.e. Given a user's login dates, find out if they were logged in 5 or more times in 30 days.

extension Date {
    static func parse(_ str: String) -> Date {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd"
        return dateFormatter.date(from: str)!
    }

    func format() -> String {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd"
        return dateFormatter.string(from: self)
    }
}

let dates: [Date] = [
    .parse("2000-01-01"),
    .parse("2000-01-02"),
    .parse("2000-01-03"),
    .parse("2000-01-04"),

    .parse("2000-02-06"),
    .parse("2000-02-07"),
    .parse("2000-02-08"),
    .parse("2000-02-09"),
    .parse("2000-02-10"),
]

let MONTH : TimeInterval = 30 * 24 * 3600

func matching(_ dates: [Date]) -> Bool {
    for ix in (0..<dates.count - 4) {
        if dates[ix + 4].timeIntervalSince(dates[ix]) < MONTH {
            print("Matched with \(dates[ix].format()) \(dates[ix + 4].format())")
            return true
        }
    }
    return false
}


print(matching(dates) ? "YEP" : "NOPE")

Output

2000-01-01	2000-01-01	false	0
2000-01-02	2000-01-01	false	1
2000-01-03	2000-01-01	false	2
2000-01-04	2000-01-01	false	3
2000-01-05	2000-01-01	false	4
Matched at 2000-01-05 08:00:00 +0000
YEP

After removing 2000-01-05

Output

2000-01-01	2000-01-01	false	0
2000-01-02	2000-01-01	false	1
2000-01-03	2000-01-01	false	2
2000-01-04	2000-01-01	false	3
2000-02-06	2000-01-01	true	4
2000-02-06	2000-01-01	true	4	inside
2000-02-06	2000-01-02	true	3	inside
2000-02-06	2000-01-03	true	2	inside
2000-02-06	2000-01-04	true	1	inside
2000-02-07	2000-02-06	false	1
2000-02-08	2000-02-06	false	2
2000-02-09	2000-02-06	false	3
2000-02-10	2000-02-06	false	4
Matched at 2000-02-10 08:00:00 +0000
YEP

New version output (with 2000-01-05 removed):

Matched with 2000-02-06 2000-02-10
YEP