From a23086ebff179315d49d54cab793121b37e100e8 Mon Sep 17 00:00:00 2001
From: Simmo Saan <simmo.saan@gmail.com>
Date: Thu, 12 Dec 2024 08:35:55 +0200
Subject: [PATCH] Solve 2024 day 12 part 2

---
 .../eu/sim642/adventofcode2024/Day12.scala    | 56 +++++++++++++++++--
 .../sim642/adventofcode2024/Day12Test.scala   | 35 ++++++++++--
 2 files changed, 81 insertions(+), 10 deletions(-)

diff --git a/src/main/scala/eu/sim642/adventofcode2024/Day12.scala b/src/main/scala/eu/sim642/adventofcode2024/Day12.scala
index 860b2bd8..49964a45 100644
--- a/src/main/scala/eu/sim642/adventofcode2024/Day12.scala
+++ b/src/main/scala/eu/sim642/adventofcode2024/Day12.scala
@@ -5,9 +5,12 @@ import eu.sim642.adventofcodelib.GridImplicits.*
 import eu.sim642.adventofcodelib.box.Box
 import eu.sim642.adventofcodelib.graph.{BFS, GraphComponents}
 import eu.sim642.adventofcodelib.pos.Pos
+import eu.sim642.adventofcode2018.Day13.DirectionPos
 
 object Day12 {
 
+  case class Edge(in: Pos, out: Pos)
+
   case class Region(poss: Set[Pos]) {
     def area: Int = poss.size
 
@@ -17,6 +20,34 @@ object Day12 {
         .map(pos => Pos.axisOffsets.map(pos + _).count(poss)) //.tapEach(println)
         .sum
     }
+
+    def sides: Int = {
+      val edges =
+        for {
+          pos <- poss
+          offset <- Pos.axisOffsets
+          newPos = pos + offset
+          if !poss(newPos)
+        } yield Edge(pos, newPos)
+
+      val graphComponents = new GraphComponents[Edge] {
+        override def nodes: IterableOnce[Edge] = edges
+
+        override def unitNeighbors(edge: Edge): IterableOnce[Edge] = {
+          val Edge(in, out) = edge
+          val direction = out - in
+          for {
+            inOffset <- Seq(direction.left, direction.right)
+            newIn = in + inOffset
+            newOut = newIn + direction
+            newEdge = Edge(newIn, newOut)
+            if edges(newEdge)
+          } yield newEdge
+        }
+      }
+
+      BFS.components(graphComponents).size
+    }
   }
 
   def regions(grid: Grid[Char]): Set[Region] = {
@@ -37,11 +68,23 @@ object Day12 {
     BFS.components(graphComponents).map(x => Region(x.toSet)).toSet // TODO: avoid weird toSet-s
   }
 
-  def totalFencingPrice(grid: Grid[Char]): Int = {
-    val regs = regions(grid)
-    //for (region <- regs)
-    //  println(s"${grid(region.poss.head)}: area=${region.area} perimeter=${region.perimeter}")
-    regs.iterator.map(region => region.area * region.perimeter).sum
+  trait Part {
+    def regionFencingPrice(region: Region): Int
+
+    def totalFencingPrice(grid: Grid[Char]): Int = {
+      val regs = regions(grid)
+      //for (region <- regs)
+      //  println(s"${grid(region.poss.head)}: area=${region.area} perimeter=${region.perimeter}")
+      regs.iterator.map(regionFencingPrice).sum
+    }
+  }
+
+  object Part1 extends Part {
+    override def regionFencingPrice(region: Region): Int = region.area * region.perimeter
+  }
+
+  object Part2 extends Part {
+    override def regionFencingPrice(region: Region): Int = region.area * region.sides
   }
 
   def parseGrid(input: String): Grid[Char] = input.linesIterator.map(_.toVector).toVector
@@ -49,6 +92,7 @@ object Day12 {
   lazy val input: String = scala.io.Source.fromInputStream(getClass.getResourceAsStream("day12.txt")).mkString.trim
 
   def main(args: Array[String]): Unit = {
-    println(totalFencingPrice(parseGrid(input)))
+    println(Part1.totalFencingPrice(parseGrid(input)))
+    println(Part2.totalFencingPrice(parseGrid(input)))
   }
 }
diff --git a/src/test/scala/eu/sim642/adventofcode2024/Day12Test.scala b/src/test/scala/eu/sim642/adventofcode2024/Day12Test.scala
index 17204528..f0eecbba 100644
--- a/src/test/scala/eu/sim642/adventofcode2024/Day12Test.scala
+++ b/src/test/scala/eu/sim642/adventofcode2024/Day12Test.scala
@@ -30,13 +30,40 @@ class Day12Test extends AnyFunSuite {
       |MIIISIJEEE
       |MMMISSJEEE""".stripMargin
 
+  val exampleInput4 =
+    """EEEEE
+      |EXXXX
+      |EEEEE
+      |EXXXX
+      |EEEEE""".stripMargin
+
+  val exampleInput5 =
+    """AAAAAA
+      |AAABBA
+      |AAABBA
+      |ABBAAA
+      |ABBAAA
+      |AAAAAA""".stripMargin
+
   test("Part 1 examples") {
-    assert(totalFencingPrice(parseGrid(exampleInput)) == 140)
-    assert(totalFencingPrice(parseGrid(exampleInput2)) == 772)
-    assert(totalFencingPrice(parseGrid(exampleInput3)) == 1930)
+    assert(Part1.totalFencingPrice(parseGrid(exampleInput)) == 140)
+    assert(Part1.totalFencingPrice(parseGrid(exampleInput2)) == 772)
+    assert(Part1.totalFencingPrice(parseGrid(exampleInput3)) == 1930)
   }
 
   test("Part 1 input answer") {
-    assert(totalFencingPrice(parseGrid(input)) == 1433460)
+    assert(Part1.totalFencingPrice(parseGrid(input)) == 1433460)
+  }
+
+  test("Part 2 examples") {
+    assert(Part2.totalFencingPrice(parseGrid(exampleInput)) == 80)
+    assert(Part2.totalFencingPrice(parseGrid(exampleInput2)) == 436)
+    assert(Part2.totalFencingPrice(parseGrid(exampleInput4)) == 236)
+    assert(Part2.totalFencingPrice(parseGrid(exampleInput5)) == 368)
+    assert(Part2.totalFencingPrice(parseGrid(exampleInput3)) == 1206)
+  }
+
+  test("Part 2 input answer") {
+    assert(Part2.totalFencingPrice(parseGrid(input)) == 855082)
   }
 }