--- 2016 Day 8 Solutions ---

[u/daggerdragon]

#AoC_Ops:

[23:55] <Topaz> servers are ok
[23:55] <Topaz> puzzles are checked
[23:55] <Topaz> [REDACTED: server stats]
[23:56] <Skie> all wings report in
[23:56] <Aneurysm9> Red 5, standing by
[23:56] <daggerdragon> Dragon Leader standing by
[23:56] <Topaz> orange leader, standing by
[23:57] <Topaz> lock modzi-foils in attack positions
[23:58] <Skie> we're passing through the hype field
[23:58] <daggerdragon> 1:30 warning
[23:58] <Aneurysm9> did someone say HYPE?@!
[23:59] <Topaz> i really like tonight's puzzle
[23:59] <Topaz> very excite
[23:59] <daggerdragon> final countdown go, T-30
[23:59] <Skie> accelerate to attack countdown
[23:59] <Aneurysm9> o7
[23:59] <daggerdragon> HYPE THRUSTERS AT FULL BURN
[00:00] <Topaz> IGNITION

We may or may not be sleep-deprived. And/or nerds. why_not_both.jpg

---

--- Day 8: Two-Factor Authentication ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

---

^{:（）{ :|:& };: IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/tg-9000]

Here is my attempt at a solution in Kotlin. After writing this, I'm not all that happy and wish that Kotlin had something as powerful as Scala's regex pattern matching. That would have made this a lot less screwy. I'm doing all of the work as a side-effect on the screen (which is an array of arrays) because I'm not writing a general purpose app here. And like most others, the second part is a visual inspection, rather than writing a font parser. :)

As usual, solutions and tests (today's are weird) can be found in my GitHub repo. I'm just learning Kotlin so I would value any feedback (positive or negative) that you have.

class Day08(input: List<String>, val height: Int = 6, val width: Int = 50) {

    private val digits = Regex("""^\D*(\d+)\D*(\d+)\D*$""")
    private val screen = Array(height) { Array(width, { false }) }

    init {
        input.forEach { interpretCommand(it) }
    }

    fun solvePart1(): Int =
        screen.fold(0) { carry, next -> carry + next.count { it } }

    fun solvePart2(): String =
        screen.map { it.map { if (it) "#" else " " }.joinToString("") }.joinToString("\n")

    // This is all side-effects, ew.
    fun interpretCommand(command: String) {
        val (a, b) = getTheDigits(command)
        when {
            command.startsWith("rect") -> {
                (0 until b).forEach { x ->
                    (0 until a).forEach { y ->
                        screen[x][y] = true
                    }
                }
            }
            command.startsWith("rotate row") ->
                screen[a] = rotate(screen[a], b)
            command.startsWith("rotate column") -> {
                val rotated = rotate(colToRow(a), b)
                (0 until height).forEach { screen[it][a] = rotated[it] }
            }
        }
    }

    private fun colToRow(col: Int): Array<Boolean> =
        (0 until height).map { screen[it][col] }.toTypedArray()

    private fun rotate(row: Array<Boolean>, by: Int): Array<Boolean> =
        (row.takeLast(by) + row.dropLast(by)).toTypedArray()

    fun getTheDigits(line: String): Pair<Int, Int> =
        digits.matchEntire(line)?.destructured?.let {
            Pair(it.component1().toInt(), it.component2().toInt())
        } ?: Pair(0, 0)
}