day 6 puzzle 2

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)
+  }
+}
+