1 files changed, 113 insertions, 0 deletions
diff --git a/aoc2023-gleam/src/day18/solve.gleam b/aoc2023-gleam/src/day18/solve.gleam
new file mode 100644
index 0000000..2c000f9
--- /dev/null
+++ b/aoc2023-gleam/src/day18/solve.gleam
@@ -0,0 +1,113 @@
+import adglent.{First, Second}
+import gleam/io
+import gleam/int
+import gleam/list
+import gleam/option.{Some}
+import gleam/regex.{type Match, Match}
+import gleam/string
+
+type Coord {
+  Coord(x: Int, y: Int)
+}
+
+type Direction {
+  Up
+  Right
+  Down
+  Left
+}
+
+type Dig {
+  Dig(dir: Direction, dist: Int)
+}
+
+fn to_direction(c: String) {
+  case c {
+    "R" | "0" -> Right
+    "D" | "1" -> Down
+    "L" | "2" -> Left
+    "U" | "3" -> Up
+    _ -> panic
+  }
+}
+
+fn parse_front(line: String) {
+  let assert Ok(re) = regex.from_string("(.) (.*) \\(.*\\)")
+  let assert [Match(submatches: [Some(dir), Some(dist)], ..)] =
+    regex.scan(with: re, content: line)
+  let assert Ok(n) = int.parse(dist)
+  Dig(to_direction(dir), n)
+}
+
+fn parse_hex(line: String) {
+  let assert Ok(re) = regex.from_string("\\(#(.....)(.)\\)")
+  let assert [Match(submatches: [Some(dist), Some(dir)], ..)] =
+    regex.scan(with: re, content: line)
+  let assert Ok(n) = int.base_parse(dist, 16)
+  Dig(to_direction(dir), n)
+}
+
+fn go(current: Coord, dig: Dig) {
+  case dig {
+    Dig(Up, n) -> Coord(current.x, current.y + n)
+    Dig(Right, n) -> Coord(current.x + n, current.y)
+    Dig(Down, n) -> Coord(current.x, current.y - n)
+    Dig(Left, n) -> Coord(current.x - n, current.y)
+  }
+}
+
+fn double_triangle(c1: Coord, c2: Coord) {
+  { c1.x * c2.y } - { c2.x * c1.y }
+}
+
+fn start_dig(digs: List(Dig)) {
+  do_next_dig(digs, Coord(0, 0), 0, 0)
+}
+
+fn do_next_dig(
+  digs: List(Dig),
+  current: Coord,
+  area: Int,
+  perimeter: Int,
+) -> Int {
+  case digs {
+    [] -> int.absolute_value(area) / 2 + { perimeter / 2 } + 1
+    [dig, ..rest] -> {
+      let next = go(current, dig)
+      let area = area + double_triangle(current, next)
+      let perimeter = perimeter + dig.dist
+      do_next_dig(rest, next, area, perimeter)
+    }
+  }
+}
+
+fn solve_with(input, f) {
+  input
+  |> string.split("\n")
+  |> list.map(f)
+  |> start_dig
+  |> string.inspect
+}
+
+pub fn part1(input: String) {
+  solve_with(input, parse_front)
+}
+
+pub fn part2(input: String) {
+  solve_with(input, parse_hex)
+}
+
+pub fn main() {
+  let assert Ok(part) = adglent.get_part()
+  let assert Ok(input) = adglent.get_input("18")
+  case part {
+    First ->
+      part1(input)
+      |> adglent.inspect
+      |> io.println
+    Second ->
+      part2(input)
+      |> adglent.inspect
+      |> io.println
+  }
+}