Advent2019_Day1.swift

import Foundation

func cost(_ mass: Int) -> Int {
    return (mass/3) - 2
}

func moduleCost(_ mass: Int, _ sum: Int = 0) -> Int {
    let remainder = cost(mass)
    let sum = sum + remainder
    if cost(remainder) <= 0 {
        return sum
    }
    return moduleCost(remainder, sum)
}

func totalFuelCost(fileURL: URL) throws -> Int {
    return try String(contentsOf: fileURL)
        .split(separator: "\n")
        .map{ line in Int(String(line))! }
        .map{ mass in moduleCost(mass) }
        .reduce(0,+)
}

try totalFuelCost(fileURL: #fileLiteral(resourceName: "Day 1.txt"))