Day 07

aoc/src/dev/ctsk/aoc/Main.scala

@@ -8,7 +8,8 @@ val solvers = Map[Int, Solver](
   3 -> Day03,
   4 -> Day04,
   5 -> Day05,
-  6 -> Day06
+  6 -> Day06,
+  7 -> Day07
 )
 
 def runSolver(solver: Solver, input: os.Path): Unit =

aoc/src/dev/ctsk/aoc/Util.scala

@@ -0,0 +1,6 @@
+package dev.ctsk.aoc
+
+def NAT_REGEX = """(\d+)""".r
+
+def longs(string: String): Vector[Long] =
+  NAT_REGEX.findAllIn(string).map(_.toLong).toVector

aoc/src/dev/ctsk/aoc/days/Day07.scala

@@ -0,0 +1,39 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc._
+
+object Day07 extends Solver(7):
+  def concat(a: Long, b: Long): Long =
+    var m: Long = 1
+    while m * 10 <= b do m *= 10
+    a * (m * 10) + b
+
+  class Searcher(target: Long, nums: Vector[Long], elephants: Boolean):
+    def search(acc: Long = nums(1), pos: Int = 2): Boolean =
+      if (pos >= nums.length) acc == target
+      else if (acc > target) false
+      else
+        search(acc + nums(pos), pos + 1) || search(acc * nums(pos), pos + 1)
+        || (elephants && search(concat(acc, nums(pos)), pos + 1))
+
+  def run(input: os.ReadablePath): (Timings, Solution) =
+    val (pre_time, in) = timed { os.read.lines(input).map(longs).toVector }
+
+    val (p1_time, p1_solution) = timed {
+      in
+        .filter(nums => Searcher(nums(0), nums, false).search())
+        .map(_.head)
+        .sum
+    }
+
+    val (p2_time, p2_solution) = timed {
+      in
+        .filter(nums => Searcher(nums(0), nums, true).search())
+        .map(_.head)
+        .sum
+    }
+
+    (
+      Timings(pre_time, p1_time, p2_time),
+      Solution(Long.box(p1_solution), Long.box(p2_solution))
+    )