Year 2015 Day 20

Author: maneatingape

README.md

@@ -229,3 +229,4 @@ The minimal SBT project provides:
 | 17 | [No Such Thing as Too Much](https://adventofcode.com/2015/day/17) | [Source](src/main/scala/AdventOfCode2015/Day17.scala) |
 | 18 | [Like a GIF For Your Yard](https://adventofcode.com/2015/day/18) | [Source](src/main/scala/AdventOfCode2015/Day18.scala) |
 | 19 | [Medicine for Rudolph](https://adventofcode.com/2015/day/19) | [Source](src/main/scala/AdventOfCode2015/Day19.scala) |
+| 20 | [Infinite Elves and Infinite Houses](https://adventofcode.com/2015/day/20) | [Source](src/main/scala/AdventOfCode2015/Day20.scala) |

src/main/resources/AdventOfCode2015/Day20.txt

@@ -0,0 +1 @@
+29000000

src/main/scala/AdventOfCode2015/Day20.scala

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+package AdventOfCode2015
+
+object Day20:
+  def part1(target: Int): Int =
+    val limit = target / 10
+    val houses = Array.fill(limit + 1)(10)
+    for x <- 2 to limit; y <- x to limit by x do houses(y) += 10 * x
+    houses.indexWhere(_ >= target)
+
+  def part2(target: Int): Int =
+    val limit = target / 10
+    val houses = Array.fill(limit + 1)(10)
+    for x <- 2 to limit; y <- (x to limit by x).take(50) do houses(y) += 11 * x
+    houses.indexWhere(_ >= target)
+
+  def main(args: Array[String]): Unit =
+    val data = io.Source.fromResource("AdventOfCode2015/Day20.txt").mkString.trim.toInt
+    println(part1(data))
+    println(part2(data))

src/test/scala/AdventOfCode2015/Day20Suite.scala

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+package AdventOfCode2015
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Day20Suite extends AnyFunSuite
+// No unit tests possible