❇️ day 6

src/main/resources/year2023/day06.txt

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+Time:        44     70     70     80
+Distance:   283   1134   1134   1491

src/main/scala/org/lemon/advent/year2023/Day06.scala

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+package org.lemon.advent.year2023
+
+private object Day06:
+  def parse(input: String) =
+    val ins = input.linesIterator
+      .map(_ match
+        case s"$_: $nums" => nums.split(" ").map(_.trim).map(_.toLongOption).flatten.toSeq
+      )
+      .toSeq
+    ins(0).zip(ins(1))
+
+  def quadratic(time: Long, dist: Long) =
+    val (a, b, c) = (-1, time, -(dist + 1)) // dist+1 because we need to beat them
+    val t1 = (-b + math.sqrt(b * b - 4 * a * c)) / (2 * a)
+    val t2 = (-b - math.sqrt(b * b - 4 * a * c)) / (2 * a)
+    println((t1, t2))
+    if t1.isNaN || t2.isNaN then 0
+    else (math.floor(math.max(t1, t2)) - math.ceil(math.min(t1, t2)) + 1).toLong
+
+  def part1(input: String) = parse(input)
+    .map(quadratic)
+    .product
+
+  def part2(input: String) =
+    val single = parse(input)
+      .map((t, d) => (t.toString, d.toString))
+      .reduce { case ((t1, d1), (t2, d2)) => (t1 + t2, d1 + d2) }
+    quadratic(single._1.toLong, single._2.toLong)

src/test/scala/org/lemon/advent/year2023/Day06Test.scala

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+package org.lemon.advent.year2023
+
+import org.lemon.advent._
+import org.lemon.advent.year2023.Day06._
+
+class Day06Test extends UnitTest:
+
+  val in = """|Time:      7  15   30
+              |Distance:  9  40  200""".stripMargin
+
+  test("part 1 example") {
+    part1(in) shouldBe 288
+  }
+
+  test("part 1") {
+    part1(read(file(2023)(6))) shouldBe 219849
+  }
+
+  test("part 2 example") {
+    part2(in) shouldBe 71503
+  }
+
+  test("part 2") {
+    part2(read(file(2023)(6))) shouldBe 29432455L
+  }