16th December solution - Advent of Code 2020 - swift

december16.swift

struct Rule {
    let name: String
    let range1: ClosedRange<Int>
    let range2: ClosedRange<Int>
    
    func contains(value: Int) -> Bool {
        return range1.contains(value) || range2.contains(value)
    }
}

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december16.txt"
let contents = try! String(contentsOfFile: filename)
var lines = contents.components(separatedBy: CharacterSet.newlines).reversed() as [String]

var rules = [Rule]()
var myTicket = [Int]()
var tickets = [[Int]]()

var line = lines.popLast()
while line?.isEmpty == false {
    let parts = line!.components(separatedBy: ": ")
    let name = parts[0]
    let ranges = parts[1].components(separatedBy: " or ")
    let range1 = ranges[0].components(separatedBy: "-")
    let range2 = ranges[1].components(separatedBy: "-")
    rules.append(Rule(name: name, range1: Int(range1[0])!...Int(range1[1])!, range2: Int(range2[0])!...Int(range2[1])!))
    line = lines.popLast()
}
line = lines.popLast()
while line?.isEmpty == false {
    if (line != "your ticket:") {
        myTicket = line!.components(separatedBy: ",").compactMap { Int($0) }
    }
    line = lines.popLast()
}
line = lines.popLast()
while line?.isEmpty == false {
    if (line != "nearby tickets:") {
        tickets.append(line!.components(separatedBy: ",").compactMap { Int($0) })
    }
    line = lines.popLast()
}

var ticketScanningErrorRate = 0
var validTickets = [[Int]]()
tickets: for ticket in tickets {
    entries: for entry in ticket {
        for rule in rules {
            if rule.contains(value: entry) {
                continue entries
            }
        }
        ticketScanningErrorRate += entry
        continue tickets
    }
    validTickets.append(ticket)
}

print(ticketScanningErrorRate)

var possiblePositionsOfRules = [String: [Int]]()
for rule in rules {
    var possiblePositions = [Int]()
    for i in 0..<20 {
        if validTickets.allSatisfy({ rule.contains(value: $0[i]) }) {
            possiblePositions.append(i)
        }
    }
    possiblePositionsOfRules[rule.name] = possiblePositions
}

var positionOfRules = [String: Int]()

var rule = possiblePositionsOfRules.first { $0.value.count == 1 }

while !possiblePositionsOfRules.allSatisfy({ $0.value.count == 1 }) {
    let entry = possiblePositionsOfRules.first { $0.value.count == 1 }!
    let position = entry.value.first!
    possiblePositionsOfRules.removeValue(forKey: entry.key)
    positionOfRules[entry.key] = position
    possiblePositionsOfRules.forEach { (key, value) in
        if value.count != 1 {
            var mutableValue = value
            mutableValue.removeAll(where: { $0 == position })
            possiblePositionsOfRules[key] = mutableValue
        }
    }
}
print(positionOfRules)
print(positionOfRules.filter { $0.key.contains("departure")}.map { myTicket[$0.value] }.reduce(1, *))