Advent2020Day10

day10.swift

public struct Day10 {

  var adapterTypes: [Bool]

  public init(input: String) {
    var parsed = Self.parse(input)
    parsed.append(0)
    adapterTypes = parsed
      .sorted()
      .slidingWindows(ofCount: 2) // import swift-algorithms
      .map { ($0.first! + 1 == $0.last!) }
  }

  static func parse(_ input: String) -> [Int] {
    input
      .split(whereSeparator: \.isNewline)
      .map { Int(String($0))! }
  }

  // MARK: - Results

  public var solve1: Int {
    let ones = adapterTypes.filter { $0 }.count
    return (adapterTypes.count - ones) * ones
  }

  public var solve2: Int {
    adapterTypes
      .split(separator: false)
      .map { $0.count }
      .map {
        if $0 == 2 { return 2 }
        if $0 == 3 { return 4 }
        if $0 == 4 { return 7 }
        return 1
      }
      .reduce(1, *)
  }
}