10th December solution - Advent of Code - swift

december10_1.swift

let countDiff = listOfDifferences.reduce(into: [:]) { counts, joltDiff in counts[joltDiff, default: 0] += 1 }

print(countDiff)

print((countDiff[1] ?? 0 ) * (countDiff[3] ?? 0 ))

december10_2.swift

let arrangementCountForConsecutiveOnes =
    [2 : 2, // 2 consecutive ones have 2 possible arrangements
     3 : 4, // 3 consecutive ones have 4 possible arrangements
     4 : 7] // 4 consecutive ones have 7 possible arrangements

var consectuiveOnesCount = [Int:Int]()
var consecutiveOnes = 0

listOfDifferences.forEach { (diff) in
    if diff == 1{
        consecutiveOnes += 1
    } else {
        if consecutiveOnes > 1 {
            consectuiveOnesCount[consecutiveOnes, default: 0] += 1
        }
        consecutiveOnes = 0
    }
}

let arragmentsCount = pow(Decimal(arrangementCountForConsecutiveOnes[2] ?? 0),consectuiveOnesCount[2] ?? 0)
    * pow(Decimal(arrangementCountForConsecutiveOnes[3] ?? 0),consectuiveOnesCount[3] ?? 0)
    * pow(Decimal(arrangementCountForConsecutiveOnes[4] ?? 0),consectuiveOnesCount[4] ?? 0)
print(arragmentsCount)

december10_shared.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december10.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines)
let numbers = lines.compactMap { Int($0) }

let targetJolts = numbers.max()! + 3

var sortedNumbers = numbers.sorted()
sortedNumbers.append(targetJolts)

var listOfDifferences = [Int]()
sortedNumbers.reduce(0) { (lastJolt, jolt) -> Int in
    listOfDifferences.append(jolt - lastJolt)
    return jolt
}