day 6 puzzle 2

README.md

@@ -5,11 +5,11 @@ This repo contains my attempt at this year's Advent of Code (2023)
 I will try and do some problems (probably not all of them) in Scala
 
 ## Progress:
-#### Stars: 11 / 50
-|        Mon        |        Tue        |     Wed     | Thu |        Fri        |        Sat        |        Sun        |
-|:-----------------:|:-----------------:|:-----------:|:---:|:-----------------:|:-----------------:|:-----------------:|
-|                   |                   |             |     | 1<br>:star::star: | 2<br>:star::star: | 3<br>:star::star: |
-| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star: |  7  |         8         |         9         |        10         |
-|        11         |        12         |     13      | 14  |        15         |        16         |        17         |
-|        18         |        19         |     20      | 21  |        22         |        23         |        24         |
-|        25         |                   |             |     |                   |                   |                   |
+#### Stars: 12 / 50
+|        Mon        |        Tue        |        Wed        | Thu |        Fri        |        Sat        |        Sun        |
+|:-----------------:|:-----------------:|:-----------------:|:---:|:-----------------:|:-----------------:|:-----------------:|
+|                   |                   |                   |     | 1<br>:star::star: | 2<br>:star::star: | 3<br>:star::star: |
+| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: |  7  |         8         |         9         |        10         |
+|        11         |        12         |        13         | 14  |        15         |        16         |        17         |
+|        18         |        19         |        20         | 21  |        22         |        23         |        24         |
+|        25         |                   |                   |     |                   |                   |                   |

src/day6/Puzzle2.scala

@@ -0,0 +1,47 @@
+package day6
+
+import scala.io.{BufferedSource, Source}
+
+object Puzzle2 {
+  case class Race(duration: Long, record: Long)
+
+  var race: Race = Race(0, 0)
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: Array[String] = source.getLines().toArray
+
+    val duration: Long = lines(0).split(": +")(1).replace(" ", "").toLong
+    val record: Long = lines(1).split(": +")(1).replace(" ", "").toLong
+
+    race = Race(duration, record)
+
+    source.close()
+  }
+
+  def getMargin(race: Race): Int = {
+    // dist = (dur - press) * press
+    // dist-record > 0 <=> f(press) = dur*press - press^2 - record > 0
+    // x^2 - d*x + r = 0
+    // x = ( d +- sqrt(d^2 - 4r) ) / 2
+
+    val delta: Double = race.duration*race.duration - 4*race.record
+    val x0: Double = (race.duration - Math.sqrt(delta))/2
+    val x1: Double = (race.duration + Math.sqrt(delta))/2
+
+    val margin: Int = (Math.ceil(x1) - Math.floor(x0) - 1).toInt
+
+    return margin
+  }
+
+  def solve(path: String): Int = {
+    loadInput(path)
+
+    return getMargin(race)
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Int = solve("./res/day6/input1.txt")
+    println(solution)
+  }
+}
+

tests/day6/Puzzle2Test.scala

@@ -0,0 +1,9 @@
+package day6
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Puzzle2Test extends AnyFunSuite {
+  test("Puzzle2.solve") {
+    assert(Puzzle2.solve("tests_res/day6/input1.txt") == 71503)
+  }
+}