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Discussion on: Advent of Code 2019 Solution Megathread - Day 1: The Tyranny of the Rocket Equation

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Replies for: My kotlin solution. import java.nio.file.Files import java.nio.file.Paths import kotlin.math.max private const val FILENAME = "src/main/resource...

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Jon Bristow •

This part 2 solution is much more elegant, and leverages monads.

tailrec fun totalFuelNeeded(mass: Int, fuel: Option<Int> = Option.empty(), totalFuel: Int = 0): Int =
    when (val nextFuel = fuel.fold({ fuelNeeded(mass) }, ::fuelNeeded)) {
        0 -> totalFuel
        else -> totalFuelNeeded(mass, nextFuel.just(), totalFuel + nextFuel)
    }