Day 8 - puzzle 1 - better.

Author: lakiboy

src/day_08/puzzle.kt

@@ -0,0 +1,62 @@
+package day_08
+
+import println
+import readInput
+
+data class Point(val x: Int, val y: Int) {
+ operator fun plus(other: Point) = Point(x + other.x, y + other.y)
+
+ operator fun times(distance: Int) = Point(x * distance, y * distance)
+}
+
+enum class Direction(val move: Point) {
+ UP(move = Point(0, -1)),
+ DOWN(move = Point(0, 1)),
+ LEFT(move = Point(-1, 0)),
+ RIGHT(move = Point(1, 0))
+}
+
+class Grid private constructor(private val trees: List<List<Int>>) {
+ private val len = trees.size
+
+ val visibleCount
+ get() = (len * 4 - 4) + (1 until (len - 1)).sumOf { y ->
+ (1 until (len - 1)).count { x -> Point(x, y).visible }
+ }
+
+ private val Point.visible get() = Direction.values().any { visibleTowards(it.move, 1) }
+
+ private val Point.value get() = trees[y][x]
+
+ private val Point.edge get() = x == 0 || y == 0 || x == len - 1 || y == len - 1
+
+ private tailrec fun Point.visibleTowards(move: Point, distance: Int): Boolean {
+ val neighbour = move * distance + this
+
+ return when {
+ neighbour.value >= value -> false
+ neighbour.edge -> true
+ else -> visibleTowards(move, distance + 1)
+ }
+ }
+
+ companion object {
+ fun of(lines: List<String>): Grid {
+ val trees = lines.map { row ->
+ row.map { it.digitToInt() }
+ }
+
+ return Grid(trees)
+ }
+ }
+}
+
+fun puzzle1(lines: List<String>) = Grid.of(lines).visibleCount
+
+fun main() {
+ val testInput = readInput("day_08/input_test")
+ check(puzzle1(testInput) == 21)
+
+ val input = readInput("day_08/input")
+ puzzle1(input).println()
+}

src/day_08_dumb/puzzle.kt

@@ -1,4 +1,4 @@
-package day_08
+package day_08_dumb
 
 // Dumb: no optimization, no cache, no tail recursion.