day 6

gleam.toml

@@ -5,6 +5,7 @@ version = "1.0.0"
 gleam_stdlib = ">= 0.34.0 and < 2.0.0"
 stdin = ">= 1.1.4 and < 2.0.0"
 gleam_yielder = ">= 1.1.0 and < 2.0.0"
+parallel_map = ">= 2.1.0 and < 3.0.0"
 
 [dev-dependencies]
 gleeunit = ">= 1.0.0 and < 2.0.0"

manifest.toml

@@ -2,9 +2,12 @@
 # You typically do not need to edit this file
 
 packages = [
+  { name = "gleam_erlang", version = "0.33.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "A1D26B80F01901B59AABEE3475DD4C18D27D58FA5C897D922FCB9B099749C064" },
+  { name = "gleam_otp", version = "0.14.1", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_stdlib"], otp_app = "gleam_otp", source = "hex", outer_checksum = "5A8CE8DBD01C29403390A7BD5C0A63D26F865C83173CF9708E6E827E53159C65" },
   { name = "gleam_stdlib", version = "0.45.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "206FCE1A76974AECFC55AEBCD0217D59EDE4E408C016E2CFCCC8FF51278F186E" },
   { name = "gleam_yielder", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_yielder", source = "hex", outer_checksum = "8E4E4ECFA7982859F430C57F549200C7749823C106759F4A19A78AEA6687717A" },
   { name = "gleeunit", version = "1.2.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "F7A7228925D3EE7D0813C922E062BFD6D7E9310F0BEE585D3A42F3307E3CFD13" },
+  { name = "parallel_map", version = "2.1.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_otp", "gleam_stdlib"], otp_app = "parallel_map", source = "hex", outer_checksum = "DE2BA9878728EF9EE34BE83FEDC7A18A1ABE4B2AC1E79C710E3E5D95F5E73404" },
   { name = "stdin", version = "1.1.4", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "stdin", source = "hex", outer_checksum = "04C04035F2A4CEEFB023837249649CD25F9A9CF5A45F9947C4D0462428A4677D" },
 ]
 
@@ -12,4 +15,5 @@ packages = [
 gleam_stdlib = { version = ">= 0.34.0 and < 2.0.0" }
 gleam_yielder = { version = ">= 1.1.0 and < 2.0.0" }
 gleeunit = { version = ">= 1.0.0 and < 2.0.0" }
+parallel_map = { version = ">= 2.1.0 and < 3.0.0" }
 stdin = { version = ">= 1.1.4 and < 2.0.0" }

sample/day6-sample.txt

@@ -0,0 +1,10 @@
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...

src/day6_p1.gleam

@@ -0,0 +1,137 @@
+import gleam/io
+import gleam/iterator
+import gleam/list.{filter, map}
+import gleam/pair
+import gleam/result
+import gleam/string
+import stdin.{stdin}
+
+pub fn main() {
+  stdin()
+  |> read_input
+  |> traverse
+  |> io.debug
+}
+
+fn traverse(params: #(Map, #(Int, Int))) -> Int {
+  let #(map, guard) = params
+
+  traverse_loop([], map, guard, Up)
+  |> list.unique
+  |> list.length
+}
+
+fn traverse_loop(
+  visited: List(#(Int, Int)),
+  map: Map,
+  position: #(Int, Int),
+  direction: Direction,
+) -> List(#(Int, Int)) {
+  case position {
+    #(x, _) if x < 0 -> visited
+    #(x, _) if x >= map.width -> visited
+    #(_, y) if y < 0 -> visited
+    #(_, y) if y >= map.height -> visited
+    _ -> {
+      let next = walk(position, direction)
+      case
+        map.obstacles
+        |> list.find(fn(x) { x == next })
+      {
+        Ok(_) -> traverse_loop(visited, map, position, turn(direction))
+        _ -> traverse_loop([position, ..visited], map, next, direction)
+      }
+    }
+  }
+}
+
+type Direction {
+  Up
+  Left
+  Right
+  Down
+}
+
+fn walk(pos: #(Int, Int), dir: Direction) -> #(Int, Int) {
+  let #(x, y) = pos
+  case dir {
+    Up -> #(x, y - 1)
+    Down -> #(x, y + 1)
+    Left -> #(x - 1, y)
+    Right -> #(x + 1, y)
+  }
+}
+
+fn turn(dir: Direction) -> Direction {
+  case dir {
+    Up -> Right
+    Right -> Down
+    Down -> Left
+    Left -> Up
+  }
+}
+
+type Map {
+  Map(width: Int, height: Int, obstacles: List(#(Int, Int)))
+}
+
+fn read_input(it: iterator.Iterator(String)) -> #(Map, #(Int, Int)) {
+  let maptxt =
+    it
+    |> iterator.to_list
+    |> map(string.trim)
+    |> filter(not(string.is_empty))
+
+  let assert Ok(width) = list.first(maptxt) |> result.map(string.length)
+  let height = list.length(maptxt)
+  let obstacles = maptxt |> list.index_fold([], find_obstacles)
+
+  let assert Ok(guard) =
+    maptxt
+    |> find_index(fn(line, y) {
+      use x <- result.try(
+        line
+        |> string.to_graphemes
+        |> find_index(fn(chr, x) {
+          case chr {
+            "^" -> Ok(x)
+            _ -> Error(Nil)
+          }
+        }),
+      )
+      Ok(#(x, y))
+    })
+
+  #(Map(width, height, obstacles), guard)
+}
+
+fn find_obstacles(
+  acc: List(#(Int, Int)),
+  line: String,
+  y: Int,
+) -> List(#(Int, Int)) {
+  line
+  |> string.to_graphemes
+  |> list.index_fold(acc, fn(cur, chr, x) {
+    case chr {
+      "#" -> [#(x, y), ..cur]
+      _ -> cur
+    }
+  })
+}
+
+fn find_index(
+  lst: List(a),
+  apply: fn(a, Int) -> Result(b, Nil),
+) -> Result(b, Nil) {
+  lst
+  |> list.index_map(pair.new)
+  |> list.find_map(fn(tup) {
+    let #(elem, index) = tup
+    apply(elem, index)
+  })
+}
+
+fn not(a: fn(a) -> Bool) {
+  fn(param: a) -> Bool { !a(param) }
+}

src/day6_p2.gleam

@@ -0,0 +1,172 @@
+import gleam/dict.{type Dict}
+import gleam/int
+import gleam/io
+import gleam/iterator
+import gleam/list.{filter, map}
+import gleam/pair
+import gleam/result
+import gleam/string
+import parallel_map
+import stdin.{stdin}
+
+pub fn main() {
+  stdin()
+  |> read_input
+  |> obstruct
+  |> io.debug
+}
+
+fn obstruct(params: #(Map, #(Int, Int))) -> Int {
+  let #(map, guard) = params
+
+  // Skip first step (guard starting spot)
+  let assert Finite([_, ..steps]) =
+    traverse_loop_check(dict.new(), map, guard, Up)
+
+  // Beware, this one takes a while...
+  steps
+  |> parallel_map.list_pmap(
+    fn(obstruction) {
+      let new_map = Map(map.width, map.height, [obstruction, ..map.obstacles])
+      traverse_loop_check(dict.new(), new_map, guard, Up)
+    },
+    parallel_map.MatchSchedulersOnline,
+    5000,
+  )
+  |> list.count(fn(x) { x == Ok(Loop) })
+}
+
+type Patrol {
+  Finite(visited: List(#(Int, Int)))
+  Loop
+}
+
+fn traverse_loop_check(
+  visited: Dict(#(#(Int, Int), Direction), Int),
+  map: Map,
+  position: #(Int, Int),
+  direction: Direction,
+) -> Patrol {
+  case dict.has_key(visited, #(position, direction)) {
+    True -> Loop
+    False ->
+      case position {
+        #(x, _) if x < 0 -> Finite(visited |> to_steps)
+        #(x, _) if x >= map.width -> Finite(visited |> to_steps)
+        #(_, y) if y < 0 -> Finite(visited |> to_steps)
+        #(_, y) if y >= map.height -> Finite(visited |> to_steps)
+        _ -> {
+          let next = walk(position, direction)
+          case
+            map.obstacles
+            |> list.find(fn(x) { x == next })
+          {
+            Ok(_) ->
+              traverse_loop_check(visited, map, position, turn(direction))
+            _ ->
+              traverse_loop_check(
+                visited |> dict.insert(#(position, direction), 1),
+                map,
+                next,
+                direction,
+              )
+          }
+        }
+      }
+  }
+}
+
+fn to_steps(visited: Dict(#(a, _), _)) -> List(a) {
+  visited |> dict.keys |> list.map(pair.first) |> list.unique
+}
+
+type Direction {
+  Up
+  Left
+  Right
+  Down
+}
+
+fn walk(pos: #(Int, Int), dir: Direction) -> #(Int, Int) {
+  let #(x, y) = pos
+  case dir {
+    Up -> #(x, y - 1)
+    Down -> #(x, y + 1)
+    Left -> #(x - 1, y)
+    Right -> #(x + 1, y)
+  }
+}
+
+fn turn(dir: Direction) -> Direction {
+  case dir {
+    Up -> Right
+    Right -> Down
+    Down -> Left
+    Left -> Up
+  }
+}
+
+type Map {
+  Map(width: Int, height: Int, obstacles: List(#(Int, Int)))
+}
+
+fn read_input(it: iterator.Iterator(String)) -> #(Map, #(Int, Int)) {
+  let maptxt =
+    it
+    |> iterator.to_list
+    |> map(string.trim)
+    |> filter(not(string.is_empty))
+
+  let assert Ok(width) = list.first(maptxt) |> result.map(string.length)
+  let height = list.length(maptxt)
+  let obstacles = maptxt |> list.index_fold([], find_obstacles)
+
+  let assert Ok(guard) =
+    maptxt
+    |> find_index(fn(line, y) {
+      use x <- result.try(
+        line
+        |> string.to_graphemes
+        |> find_index(fn(chr, x) {
+          case chr {
+            "^" -> Ok(x)
+            _ -> Error(Nil)
+          }
+        }),
+      )
+      Ok(#(x, y))
+    })
+
+  #(Map(width, height, obstacles), guard)
+}
+
+fn find_obstacles(
+  acc: List(#(Int, Int)),
+  line: String,
+  y: Int,
+) -> List(#(Int, Int)) {
+  line
+  |> string.to_graphemes
+  |> list.index_fold(acc, fn(cur, chr, x) {
+    case chr {
+      "#" -> [#(x, y), ..cur]
+      _ -> cur
+    }
+  })
+}
+
+fn find_index(
+  lst: List(a),
+  apply: fn(a, Int) -> Result(b, Nil),
+) -> Result(b, Nil) {
+  lst
+  |> list.index_map(pair.new)
+  |> list.find_map(fn(tup) {
+    let #(elem, index) = tup
+    apply(elem, index)
+  })
+}
+
+fn not(a: fn(a) -> Bool) {
+  fn(param: a) -> Bool { !a(param) }
+}