day 6 puzzle 1

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: 10 / 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  |  7  |         8         |         9         |        10         |
-|        11         |        12         | 13  | 14  |        15         |        16         |        17         |
-|        18         |        19         | 20  | 21  |        22         |        23         |        24         |
-|        25         |                   |     |     |                   |                   |                   |
+#### 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         |                   |             |     |                   |                   |                   |

src/day6/Puzzle1.scala

@@ -0,0 +1,54 @@
+package day6
+
+import scala.io.{BufferedSource, Source}
+
+object Puzzle1 {
+  case class Race(duration: Int, record: Int)
+
+  var races: Array[Race] = Array.empty
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: Array[String] = source.getLines().toArray
+
+    val durations: Array[Int] = lines(0).split(": +")(1).split(" +").map(d => d.toInt)
+    val records: Array[Int] = lines(1).split(": +")(1).split(" +").map(r => r.toInt)
+
+    races = new Array(durations.length)
+
+    for (i: Int <- races.indices) {
+      races(i) = Race(durations(i), records(i))
+    }
+
+    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)
+
+    var solution: Int = 1
+    for (race: Race <- races) {
+      solution *= getMargin(race)
+    }
+
+    return solution
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Int = solve("./res/day6/input1.txt")
+    println(solution)
+  }
+}

tests/day6/Puzzle1Test.scala

@@ -0,0 +1,9 @@
+package day6
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Puzzle1Test extends AnyFunSuite {
+  test("Puzzle1.solve") {
+    assert(Puzzle1.solve("tests_res/day6/input1.txt") == 288)
+  }
+}

tests_res/day6/input1.txt

@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200