6th December solution - Advent of Code - swift

december06_1.swift

let solution = solve(lines, isFirstPuzzle: true)
print(solution)

december06_2.swift

let solution = solve(lines, isFirstPuzzle: false)
print(solution)

december06_shared.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december06.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines)

func solve(_ lines: [String], isFirstPuzzle: Bool) -> Int {
    var group: Set<String.Element>? = nil
    var groups = [Set<String.Element>]()
    lines.forEach { (line) in
        if line.isEmpty {
            if let group = group {
                groups.append(group)
            }
            group = nil
        } else {
            if let groupNonNil = group {
                if isFirstPuzzle {
                    group = groupNonNil.union(Set(line))
                } else {
                    group = groupNonNil.intersection(Set(line))
                }
            } else {
                group = Set(line)
            }
        }
    }
    let elementsCount = groups.reduce(0) { (sum, nextSet) -> Int in
        sum + nextSet.count
    }
    return elementsCount
}