AoC 2022 Day 09

aoc202209.kt

import se.saidaspen.aoc.util.*
import kotlin.math.absoluteValue

fun main() = Day09.run()

object Day09 : Day(2022, 9) {

    override fun part1(): Any {
        var h = P(0, 0)
        var t = P(0, 0)
        val visited = mutableSetOf<P<Int, Int>>()
        visited.add(t)
        for (l in input.lines()) {
            repeat(ints(l)[0]) {
                h = move(h, l[0])
                t = move(h, t)
                visited.add(t)
            }
        }
        return visited.size
    }

    override fun part2(): Any {
        val snake =
            mutableListOf(P(0, 0), P(0, 0), P(0, 0), P(0, 0), P(0, 0), P(0, 0), P(0, 0), P(0, 0), P(0, 0), P(0, 0))
        val visited = mutableSetOf<P<Int, Int>>()
        for (l in input.lines()) {
            repeat(ints(l)[0]) {
                snake[0] = move(snake[0], l[0])
                for (i in 1 until snake.size) snake[i] = move(snake[i - 1], snake[i])
                visited.add(snake.last())
            }
        }
        return visited.size
    }

    private fun move(h: Pair<Int, Int>, dir: Char): Pair<Int, Int> {
        return when (dir) {
            'R' -> P(h.x + 1, h.y)
            'L' -> P(h.x - 1, h.y)
            'U' -> P(h.x, h.y - 1)
            'D' -> P(h.x, h.y + 1)
            else -> throw java.lang.RuntimeException("Unsupported move")
        }
    }

    private fun move(h: Pair<Int, Int>, t: Pair<Int, Int>): Pair<Int, Int> {
        var dx = h.x - t.x
        var dy = h.y - t.y
        var newT = t
        if ((dx.absoluteValue == 1 && dy.absoluteValue == 1) || (dx.absoluteValue + dy.absoluteValue < 2)) {
            return newT
        }
        
        dx = if (dx == 0) 0 else if (dx > 0) 1 else -1
        dy = if (dy == 0) 0 else if (dy > 0) 1 else -1
        if (dx == 0) {
            newT = P(t.x, t.y + dy)
        } else if (dy == 0) {
            newT = P(t.x + dx, t.y)
        } else {
            newT = P(t.x + dx, t.y + dy)
        }
        return newT
    }
}