day 23 gleam complete

3 files changed, 263 insertions, 8 deletions

diff --git a/aoc2023/src/day23/solve.gleam b/aoc2023/src/day23/solve.gleam
index 90ab62d..916ef17 100644
--- a/aoc2023/src/day23/solve.gleam
+++ b/aoc2023/src/day23/solve.gleam
@@ -1,12 +1,189 @@
 import adglent.{First, Second}
+import gleam/int
 import gleam/io
+import gleam/dict.{type Dict}
+import gleam/list
+import gleam/option.{type Option, None, Some}
+import gleam/string
+import gleam/set.{type Set}
+import gleam/bool
+import utilities/array2d.{type Array2D, type Posn, Posn}
+
+type Path {
+  Unknown
+  Straight
+  Junction
+}
+
+type Route {
+  Route(to: Posn, distance: Int)
+}
+
+fn append_to_key(v: Option(List(a)), new: a) -> List(a) {
+  case v {
+    None -> [new]
+    Some(xs) -> [new, ..xs]
+  }
+}
+
+fn first_parse_path(c: String) -> Result(Path, Nil) {
+  case c {
+    "#" -> Error(Nil)
+    _ -> Ok(Unknown)
+  }
+}
+
+fn junction_neighbors(p: Posn) -> List(Posn) {
+  [Posn(..p, r: p.r + 1), Posn(..p, c: p.c + 1)]
+}
+
+fn mark_junctions(trails: Array2D(Path)) -> Array2D(Path) {
+  use trail, _ <- dict.map_values(trails)
+
+  let valid_neighbors =
+    trail
+    |> array2d.ortho_neighbors
+    |> list.filter(dict.has_key(trails, _))
+
+  case list.length(valid_neighbors) {
+    2 -> Straight
+    _ -> Junction
+  }
+}
+
+fn start_walking_to_next_junction(
+  start: Posn,
+  next: Posn,
+  trails: Array2D(Path),
+) {
+  let seen =
+    set.new()
+    |> set.insert(start)
+    |> set.insert(next)
+  walk_to_next_junction(start, next, 1, seen, trails)
+}
+
+fn walk_to_next_junction(
+  start: Posn,
+  current: Posn,
+  length: Int,
+  seen: Set(Posn),
+  trails: Array2D(Path),
+) -> #(Posn, Route) {
+  let assert [next] =
+    current
+    |> array2d.ortho_neighbors
+    |> list.filter(fn(n) { dict.has_key(trails, n) && !set.contains(seen, n) })
+
+  case dict.get(trails, next) {
+    Ok(Junction) -> #(start, Route(to: next, distance: length + 1))
+    _ -> {
+      let seen = set.insert(seen, current)
+      walk_to_next_junction(start, next, { length + 1 }, seen, trails)
+    }
+  }
+}
+
+fn generate_routes(
+  junctions: List(Posn),
+  trails: Array2D(Path),
+) -> Dict(Posn, List(Route)) {
+  {
+    use junction <- list.flat_map(junctions)
+    use neighbor <- list.filter_map(junction_neighbors(junction))
+    case dict.has_key(trails, neighbor) {
+      True -> Ok(start_walking_to_next_junction(junction, neighbor, trails))
+      False -> Error(Nil)
+    }
+  }
+  |> list.fold(dict.new(), fn(acc, edge) {
+    let #(from, route) = edge
+    use v <- dict.update(acc, from)
+    case v {
+      None -> [route]
+      Some(routes) -> [route, ..routes]
+    }
+  })
+}
+
+fn generate_2way_routes(
+  junctions: List(Posn),
+  trails: Array2D(Path),
+) -> Dict(Posn, List(Route)) {
+  let routes = {
+    use junction <- list.flat_map(junctions)
+    use neighbor <- list.filter_map(junction_neighbors(junction))
+    case dict.has_key(trails, neighbor) {
+      True -> Ok(start_walking_to_next_junction(junction, neighbor, trails))
+      False -> Error(Nil)
+    }
+  }
+  use acc, r <- list.fold(routes, dict.new())
+  let #(from, Route(to, dist)) = r
+  acc
+  |> dict.update(from, append_to_key(_, Route(to, dist)))
+  |> dict.update(to, append_to_key(_, Route(from, dist)))
+}
+
+fn dfs(routes, from, to) {
+  let seen = set.insert(set.new(), from)
+  do_dfs(routes, from, to, 0, seen)
+}
+
+fn do_dfs(
+  routes: Dict(Posn, List(Route)),
+  from: Posn,
+  to: Posn,
+  acc: Int,
+  seen: Set(Posn),
+) -> Int {
+  use <- bool.guard(to == from, acc)
+
+  let assert Ok(all_routes) = dict.get(routes, from)
+  let neighbors = list.filter(all_routes, fn(r) { !set.contains(seen, r.to) })
+
+  case neighbors {
+    [] -> 0
+    neighbors ->
+      list.fold(neighbors, acc, fn(inner_acc, n) {
+        let score =
+          do_dfs(routes, n.to, to, acc + n.distance, set.insert(seen, n.to))
+        int.max(score, inner_acc)
+      })
+  }
+}
+
+fn solve_using(
+  input: String,
+  using: fn(List(Posn), Dict(Posn, Path)) -> Dict(Posn, List(Route)),
+) -> Int {
+  let min_row = 0
+  let max_row = list.length(string.split(input, "\n")) - 1
+
+  let trails =
+    input
+    |> array2d.parse_grid_using(first_parse_path)
+    |> mark_junctions
+
+  let junctions =
+    trails
+    |> dict.filter(fn(_, v) { v == Junction })
+    |> dict.keys
+
+  let assert Ok(start) = list.find(junctions, fn(j) { j.r == min_row })
+  let assert Ok(end) = list.find(junctions, fn(j) { j.r == max_row })
+
+  let routes = using(junctions, trails)
+
+  dfs(routes, start, end)
+}
 
 pub fn part1(input: String) {
-  todo as "Implement solution to part 1"
+  solve_using(input, generate_routes)
 }
 
 pub fn part2(input: String) {
-  todo as "Implement solution to part 2"
+  solve_using(input, generate_2way_routes)
 }
 
 pub fn main() {
diff --git a/aoc2023/src/utilities/array2d.gleam b/aoc2023/src/utilities/array2d.gleam
index 9d3b966..8538129 100644
--- a/aoc2023/src/utilities/array2d.gleam
+++ b/aoc2023/src/utilities/array2d.gleam
@@ -2,6 +2,7 @@ import gleam/list
 import gleam/dict.{type Dict}
 import gleam/string
 import gleam/int
+import gleam/result
 
 pub type Posn {
   Posn(r: Int, c: Int)
@@ -16,13 +17,29 @@ pub fn add_posns(p1: Posn, p2: Posn) -> Posn {
   }
 }
 
+pub fn ortho_neighbors(p: Posn) -> List(Posn) {
+  let Posn(r, c) = p
+  [Posn(r + 1, c), Posn(r - 1, c), Posn(r, c + 1), Posn(r, c - 1)]
+}
+
 pub fn to_2d_array(xss: List(List(a))) -> Array2D(a) {
+  to_2d_array_using(xss, fn(x) { Ok(x) })
+}
+
+pub fn to_2d_array_using(
+  xss: List(List(a)),
+  f: fn(a) -> Result(b, Nil),
+) -> Array2D(b) {
   {
     use r, row <- list.index_map(xss)
     use c, cell <- list.index_map(row)
-    #(Posn(r, c), cell)
+    case f(cell) {
+      Ok(contents) -> Ok(#(Posn(r, c), contents))
+      Error(Nil) -> Error(Nil)
+    }
   }
   |> list.flatten
+  |> result.values
   |> dict.from_list
 }
 
@@ -44,7 +61,14 @@ pub fn to_list_of_lists(str: String) -> List(List(String)) {
 }
 
 pub fn parse_grid(str: String) -> Array2D(String) {
+  parse_grid_using(str, fn(x) { Ok(x) })
+}
+
+pub fn parse_grid_using(
+  str: String,
+  f: fn(String) -> Result(a, Nil),
+) -> Array2D(a) {
   str
   |> to_list_of_lists
-  |> to_2d_array
+  |> to_2d_array_using(f)
 }
diff --git a/aoc2023/test/day23/day23_test.gleam b/aoc2023/test/day23/day23_test.gleam
index eb9496f..206571c 100644
--- a/aoc2023/test/day23/day23_test.gleam
+++ b/aoc2023/test/day23/day23_test.gleam
@@ -4,22 +4,76 @@ import adglent.{type Example, Example}
 import day23/solve
 
 type Problem1AnswerType =
-  String
+  Int
 
 type Problem2AnswerType =
-  String
+  Int
 
 /// Add examples for part 1 here:
 /// ```gleam
 ///const part1_examples: List(Example(Problem1AnswerType)) = [Example("some input", "")]
 /// ```
-const part1_examples: List(Example(Problem1AnswerType)) = []
+const part1_examples: List(Example(Problem1AnswerType)) = [
+  Example(
+    "#.#####################
+#.......#########...###
+#######.#########.#.###
+###.....#.>.>.###.#.###
+###v#####.#v#.###.#.###
+###.>...#.#.#.....#...#
+###v###.#.#.#########.#
+###...#.#.#.......#...#
+#####.#.#.#######.#.###
+#.....#.#.#.......#...#
+#.#####.#.#.#########v#
+#.#...#...#...###...>.#
+#.#.#v#######v###.###v#
+#...#.>.#...>.>.#.###.#
+#####v#.#.###v#.#.###.#
+#.....#...#...#.#.#...#
+#.#########.###.#.#.###
+#...###...#...#...#.###
+###.###.#.###v#####v###
+#...#...#.#.>.>.#.>.###
+#.###.###.#.###.#.#v###
+#.....###...###...#...#
+#####################.#",
+    94,
+  ),
+]
 
 /// Add examples for part 2 here:
 /// ```gleam
 ///const part2_examples: List(Example(Problem2AnswerType)) = [Example("some input", "")]
 /// ```
-const part2_examples: List(Example(Problem2AnswerType)) = []
+const part2_examples: List(Example(Problem2AnswerType)) = [
+  Example(
+    "#.#####################
+#.......#########...###
+#######.#########.#.###
+###.....#.>.>.###.#.###
+###v#####.#v#.###.#.###
+###.>...#.#.#.....#...#
+###v###.#.#.#########.#
+###...#.#.#.......#...#
+#####.#.#.#######.#.###
+#.....#.#.#.......#...#
+#.#####.#.#.#########v#
+#.#...#...#...###...>.#
+#.#.#v#######v###.###v#
+#...#.>.#...>.>.#.###.#
+#####v#.#.###v#.#.###.#
+#.....#...#...#.#.#...#
+#.#########.###.#.#.###
+#...###...#...#...#.###
+###.###.#.###v#####v###
+#...#...#.#.>.>.#.>.###
+#.###.###.#.###.#.#v###
+#.....###...###...#...#
+#####################.#",
+    154,
+  ),
+]
 
 pub fn part1_test() {
   part1_examples