14th December solution - Advent of Code 2020 - swift

december14_1.swift

var currentMask = ""
var memory = [Int: String]()

lines.forEach { line in
    let parts = line.components(separatedBy: " = ")
    let variable = parts[0]
    let value = parts[1]
    print(variable, value)
    if variable.contains("mask") {
        currentMask = value
    } else {
        let address = Int(variable.filter { Int(String($0)) != nil })!
        let valueDeci = Int(value)!
        let valueBinary = Array(String(valueDeci, radix: 2).padLeft(upTo: 36, char: "0"))
        var valueWithMaskApplied = ""
        for (i, maskChar) in currentMask.enumerated() {
            if maskChar == "X" {
                if i < valueBinary.count {
                    valueWithMaskApplied += String(valueBinary[i])
                } else {
                    valueWithMaskApplied += "0"
                }
            } else {
                valueWithMaskApplied += String(maskChar)
            }
        }
        memory[address] = valueWithMaskApplied
    }
}

december14_2.swift

var currentMask = ""
var memory = [Int: String]()

lines.forEach { line in
    let parts = line.components(separatedBy: " = ")
    let variable = parts[0]
    let value = parts[1]
    if variable.contains("mask") {
        currentMask = value
    } else {
        let address = Int(variable.filter { Int(String($0)) != nil })!
        let addressBinary = Array(String(address, radix: 2).padLeft(upTo: 36, char: "0"))
        let valueBinary = String(Int(value)!, radix: 2).padLeft(upTo: 36, char: "0")
        var addressWithMaskApplied = ""
        for (i, maskChar) in currentMask.enumerated() {
            if maskChar == "0" {
                addressWithMaskApplied += String(addressBinary[i])
            }
            else {
                addressWithMaskApplied += String(maskChar)
            }
        }
        let addresses = addressesReplacedX(addressBinary: addressWithMaskApplied)

        for a in addresses {
            memory[Int(a,radix: 2)!] = valueBinary
        }
    }
}


let sumOfMemory = memory.values.map { Int($0, radix: 2)! }.reduce(0, +)
print(sumOfMemory)


func addressesReplacedX(addressBinary: String) -> [String] {
    if !addressBinary.contains("X") {
        return [addressBinary]
    } else {
        let indexOfX = addressBinary.firstIndex(of: "X")!
        let firstAddress = addressBinary.replacingOccurrences(of: "X", with: "0", range: indexOfX ..< addressBinary.index(indexOfX, offsetBy: 1))
        let secondAddress = addressBinary.replacingOccurrences(of: "X", with: "1", range: indexOfX ..< addressBinary.index(indexOfX, offsetBy: 1))
        
        return addressesReplacedX(addressBinary: firstAddress) + addressesReplacedX(addressBinary: secondAddress)
    }
}

december14_shared.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december14.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty }

extension String {
    func padLeft(upTo count: Int, char: String) -> String {
        return String(String(self.reversed()).padding(toLength: count, withPad: char, startingAt: 0).reversed())
    }
}