8th December solution - Advent of Code - swift

december08_1.swift

print(runInstructions(lines: lines))

december08_2.swift

var reachedEnd = false
var changeIndex = 0
var accumulator = 0
while !reachedEnd {
    (accumulator, reachedEnd) = runInstructions(lines: lines, changeIndex: changeIndex)
    changeIndex += 1
}
print(accumulator)

december08_shared.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december08.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines)

func runInstructions(lines: [String], changeIndex: Int = -1) -> (Int, Bool) {
    var index = 0
    var linesRun = Set<Int>()
    var accumulator = 0
    var instruction = ""
    var parameter = 0
    var reachedEnd = false

    while !linesRun.contains(index) {
        linesRun.insert(index)
        if index >= lines.count - 1 {
            reachedEnd = true
            break
        }
        let line = lines[index]
        let instructionAndParameter = line.components(separatedBy: " ")
        instruction = instructionAndParameter[0]
        parameter = Int(instructionAndParameter[1])!

        if instruction == "acc" {
            accumulator += parameter
            index += 1
        } else if instruction == "jmp" {
            if index == changeIndex {
                index += 1
            } else {
                index += parameter
            }
        } else if instruction == "nop" {
            if index == changeIndex {
                index += parameter
            } else {
                index += 1
            }
        }
    }
    return (accumulator, reachedEnd)
}