class Day06(input: List<String>) {

    // Note that this is Orbiting -> Orbited, not Orbited -> Orbiting
    private val orbitPairs: Map<String, String> = input.map { it.split(")") }.associate { it.last() to it.first() }

    fun solvePart1(): Int =
        orbitPairs.keys.sumBy { pathTo(it).size }

    fun solvePart2(): Int {
        val youToRoot = pathTo("YOU")
        val santaToRoot = pathTo("SAN")
        val intersection = youToRoot.intersect(santaToRoot).first()

        return youToRoot.indexOf(intersection) + santaToRoot.indexOf(intersection) -2
    }

    private fun pathTo(orbit: String, path: MutableList<String> = mutableListOf()): MutableList<String> =
        orbitPairs[orbit]?.let {
            path.add(orbit)
            pathTo(it, path)
        } ?: path
}