Advent of Code 2018, day 2

aoc2018d2.swift

// Part 1

extension String {
    var characterCounts: [Character: Int] {
        return self.reduce(into: [Character: Int]()) { $0[$1, default: 0] += 1 }
    }
}

extension Bool {
    var intValue: Int {
        return self ? 1 : 0
    }
}

let (twos, threes) = input
    .map { $0.characterCounts.values }
    .map { ($0.contains(2).intValue, $0.contains(3).intValue) }
    .reduce((0, 0)) { ($0.0 + $1.0, $0.1 + $1.1) }
print(twos * threes)

// Part 2

extension String {
    func removingCharacter(at index: Index) -> String {
        var temp = self
        temp.removeSubrange(index...index)
        return temp
    }
}

func differences(s1: String, s2: String) -> Int {
    return zip(s1, s2).filter { $0.0 != $0.1 }.count
}

func combine(s1: String, s2: String) -> String {
    let index = s1.indices.firstIndex { s1[$0] != s2[$0] }!
    return s1.removingCharacter(at: index)
}

outside: for currentIndex in input.indices {
    for candidateIndex in (currentIndex+1..<input.endIndex) {
        let current = input[currentIndex]
        let candidate = input[candidateIndex]
        if differences(s1: current, s2: candidate) == 1 {
            print(combine(s1: current, s2: candidate))
            break outside
        }
    }
}