5th December solution - Advent of Code - swift

december05_1.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december05.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines)

let seats = lines.compactMap { seatString -> Seat? in
    if seatString.isEmpty {
        return nil
    }
    let rowEndIndex = seatString.index(seatString.startIndex, offsetBy: 7)
    let binaryRowString = String(seatString[..<rowEndIndex].map { (char) -> Character in
        char == "B" ? "1" : "0"
    })
    let row = Int(binaryRowString, radix: 2)
    let binaryColumnString = String(seatString[rowEndIndex...].map { (char) -> Character in
        char == "R" ? "1" : "0"
    })
    let column = Int(binaryColumnString, radix: 2)

    if let row = row, let column = column {
        return Seat(row: row, column: column)
    }
    return nil
}
var seatIds = seats.map { $0.seatId }
print(seatIds.max())

december05_2.swift

seatIds.sort()
seatIds.reduce(seatIds.first! - 1) { (previousSeatId, currentSeatId) -> Int in
    if previousSeatId + 1 != currentSeatId {
        print(previousSeatId + 1)
    }
    return currentSeatId
}

december05_shared.swift

struct Seat {
    let row: Int
    let column: Int
    var seatId: Int {
            get {
                return row * 8 + column
            }
        }
}