📅 Day 1️⃣7️⃣

Author: matios13

src/main/kotlin/dev/manka/advent_of_code/days/y2021/Day17.kt

@@ -0,0 +1,54 @@
+package dev.manka.advent_of_code.days.y2021
+
+import dev.manka.advent_of_code.days.Day
+import kotlin.math.absoluteValue
+import kotlin.math.sign
+
+class Day17 : Day(17, "Trick Shot") {
+
+ override fun partOne(): String {
+ val targetArea = TargetArea(inputList.first())
+ return (0..targetArea.x.last).maxOf { x ->
+ (targetArea.y.first..targetArea.y.first.absoluteValue)
+ .map { y -> trajectory((x to y)).takeWhile { !targetArea.hasOvershot(it) } }
+ .filter { it.any { p -> targetArea.has(p) } }
+ .maxOfOrNull { it.maxOf { p -> p.second } } ?: 0
+ }.toString()
+ }
+
+ override fun partTwo(): String {
+ val targetArea = TargetArea(inputList.first())
+ return (0..targetArea.x.last).sumOf { x ->
+ (targetArea.y.first..targetArea.y.first.absoluteValue)
+ .map { y -> trajectory(x to y).first { targetArea.hasOvershot(it) || targetArea.has(it) } }
+ .count { targetArea.has(it) }
+ }.toString()
+ }
+
+ private fun trajectory(velocity: Pair<Int, Int>): Sequence<Pair<Int, Int>> = sequence {
+ var x = 0
+ var y = 0
+ var Vx = velocity.first
+ var Vy = velocity.second
+ while (true) {
+ x += Vx
+ y += Vy
+ Vx += if (Vx == 0) 0 else Vx.sign * -1
+ Vy -= 1
+ yield(x to y)
+ }
+ }
+
+ private class TargetArea(input: String) {
+ val x: IntRange = input.substringAfter("=").substringBefore(".").toInt()..
+ input.substringAfter("..").substringBefore(",").toInt()
+ val y: IntRange = input.substringAfterLast("=").substringBefore(".").toInt()..
+ input.substringAfterLast(".").toInt()
+
+ fun has(point: Pair<Int, Int>): Boolean = point.first in x && point.second in y
+
+ fun hasOvershot(point: Pair<Int, Int>): Boolean = point.first > x.last || point.second < y.first
+ }
+
+
+}

src/main/resources/y2021/17.txt

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+target area: x=81..129, y=-150..-108