Day 11 part 1 and 2

README.md

@@ -77,4 +77,12 @@ Part 2: Adapt the extrapolation algorithm to use the first element of the seqque
 
 ## Day 10
 
-Part 1: From the start, find all the distances ['breadth' first](https://en.wikipedia.org/wiki/Breadth-first_search) and stop when all positions in the loop have been explored. Implemented using a LazyList.
+Part 1: From the start, find all the distances ['breadth' first](https://en.wikipedia.org/wiki/Breadth-first_search) and stop when all positions in the loop have been explored. Implemented using a LazyList.
+
+Part 2:To find the points which are inside or outside, we can count the number of intersection between an outside point and the inside point. if the number is odd, then the point is inside, if it is even then the point is outside.
+
+## Day 11
+
+Part 1: In the previous example, to store the map, I hesitated between using a two dimensional array or a map of the coordinates to the point at the location. Here as the galaxies are quite sparsed, it makes sense to only keep the coordinates. That will also help when 'expanding' the empty spaces.
+
+Part 2: Here to store the larger coordinates I used Long instead of Int. The expansion coefficient was relatively easy to add

src/main/scala/day11.scala

@@ -0,0 +1,42 @@
+import zio._
+import zio.Console._
+import Day6.nbDistances
+
+object Day11 extends ZIOAppDefault {
+
+  def findSpaces(coordinates: Set[Long]) =
+    val min = coordinates.min
+    val max = coordinates.max
+    (min to max).toSet.diff(coordinates)
+
+  def getDistance(g1: (Long, Long), g2: (Long, Long), emptyCols: Set[Long], emptyRows: Set[Long], expansion: Long) =
+    val cols =
+      (g1._1 - g2._1).abs + expansion * emptyCols.count(x => math.min(g1._1, g2._1) < x && x < math.max(g1._1, g2._1))
+    val rows =
+      (g1._2 - g2._2).abs + expansion * emptyRows.count(y => math.min(g1._2, g2._2) < y && y < math.max(g1._2, g2._2))
+    cols + rows
+
+  def part1(space: List[String], expansion: Int) =
+    val galaxies = {
+      for
+        (y, l) <- (1L to space.length) zip space
+        (x, c) <- (1L to l.length) zip l
+        if c == '#'
+      yield (x, y)
+    }.toList
+
+    val (xGalaxies, yGalaxies) = galaxies.unzip
+    val emptyCols = findSpaces(xGalaxies.toSet)
+    val emptyRows = findSpaces(yGalaxies.toSet)
+    val distances = galaxies.toList.combinations(2).map { case g1 :: g2 :: _ =>
+      getDistance(g1, g2, emptyCols, emptyRows, expansion)
+    }
+    distances.sum
+
+  def run =
+    for {
+      v <- Day1.readFile("day11_input.txt")
+      _ <- printLine(s"part1=${part1(v, 1)}")
+      _ <- printLine(s"part2=${part1(v, 999999)}")
+    } yield ()
+}

src/test/scala/day11_test.scala

@@ -0,0 +1,39 @@
+import org.junit.Test
+import org.junit.Assert._
+
+class Day11Test {
+
+  val space = """...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....""".split('\n').toList
+
+  val space2 = List("#..#..#", ".......", ".......", "......#")
+
+  @Test
+  def testFindSpaces() =
+    assertEquals(Set(3, 6, 9), Day11.findSpaces(Set(1, 2, 4, 5, 7, 8, 10)))
+
+  @Test
+  def testPart1() =
+    assertEquals(374, Day11.part1(space, 1))
+
+  @Test
+  def testPart1b() =
+    assertEquals(50, Day11.part1(space2, 1))
+
+  @Test
+  def testPart2a() =
+    assertEquals(1030, Day11.part1(space, 9))
+
+  @Test
+  def testPart2b() =
+    assertEquals(8410, Day11.part1(space, 99))
+
+}