gistfile1.txt

import UIKit

struct Domino {
  let left: Int
  let right: Int

  init(string: String) {
    let split = string.componentsSeparatedByString("-")
    left = split.first.flatMap { Int($0) } ?? 0
    right = split.last.flatMap { Int($0) } ?? 0
  }

  func matches(nextDomino: Domino) -> Bool {
    return right == nextDomino.left
  }
}

func matchCount(dominoString: String) -> Int {
  let dominoStrings = dominoString.componentsSeparatedByString(",")
  let dominos = dominoStrings.map { Domino(string: $0) }

  var matches = [Int]()
  var match: Int = 0

  for index in 0..<dominos.count {
    let domino = dominos[index]

    if index + 1 >= dominos.count {
      break
    }

    let nextDomino = dominos[index + 1]

    if domino.matches(nextDomino) {
      match += 1
    } else {
      match = 1
    }
    matches.append(match)
  }
  return matches.maxElement() ?? 1
}

matchCount("1-1,3-5,5-2,2-3,2-4")