Today was interesting. My first thought was that part 2 would be a lot more complex at first glance. But I realized that my solution for part 1 worked almost out of the box for part 2.

I was also pleased to see that the algorithm ran in 1ms, which was a good deal faster than just parsing the input.

fun main() {
    val input = getInput(3)
    val banks = parseInput(input)
    var total = 0L
    banks.forEach { bank ->
        var location = 0
        var joltage = 0L
        for (power in 11 downTo 0) {
            val multiplier = 10.toDouble().pow(power).toLong()
            val batteryLocation = findBattery(bank, location, bank.size - power - 1)
            val battery = bank[batteryLocation]
            location = batteryLocation + 1
            joltage += battery.toLong() * multiplier
        }
        total += joltage
    }
    println(total)
}

fun parseInput(input: String): List<List<Int>> = input
    .split("\n")
    .filter { it.isNotBlank() }
    .map { it.toCharArray() }
    .map { it.map { digit -> digit.digitToInt() } }

fun findBattery(bank: List<Int>, start: Int, end: Int): Int {
    var max = 0
    var location = 0
    for (i in start..end) {
        val battery = bank[i]
        if (battery > max) {
            max = battery
            location = i
            if (battery == 9) {
                break
            }
        }
    }
    return location
}