2 files changed, 85 insertions, 0 deletions
diff --git a/aoc2023/src/day13/.gitignore b/aoc2023/src/day13/.gitignore
new file mode 100644
index 0000000..ae40cea
--- /dev/null
+++ b/aoc2023/src/day13/.gitignore
@@ -0,0 +1 @@
+input.txt
+\ No newline at end of file
diff --git a/aoc2023/src/day13/solve.gleam b/aoc2023/src/day13/solve.gleam
new file mode 100644
index 0000000..a597074
--- /dev/null
+++ b/aoc2023/src/day13/solve.gleam
@@ -0,0 +1,84 @@
+import adglent.{First, Second}
+import gleam/io
+import gleam/list
+import gleam/string
+import gleam/result
+
+type SymmetryType {
+  Horizontal(Int)
+  Vertical(Int)
+}
+
+fn is_symmetric(xs: List(List(a)), errors: Int, index: Int) -> Result(Int, Nil) {
+  case list.split(xs, index) {
+    #(_, []) -> Error(Nil)
+    #(ls, rs) -> {
+      let zipped = list.zip(list.flatten(list.reverse(ls)), list.flatten(rs))
+      let found_errors =
+        zipped
+        |> list.filter(fn(tup) { tup.1 != tup.0 })
+        |> list.length
+      case found_errors == errors {
+        True -> Ok(index)
+        False -> is_symmetric(xs, errors, index + 1)
+      }
+    }
+  }
+}
+
+fn get_symmetry_type(xs: List(List(String)), errors: Int) {
+  result.or(
+    xs
+    |> is_symmetric(errors, 1)
+    |> result.map(Horizontal(_)),
+    xs
+    |> list.transpose()
+    |> is_symmetric(errors, 1)
+    |> result.map(Vertical(_)),
+  )
+}
+
+fn summarize_notes(symmetries: List(SymmetryType)) {
+  use acc, note <- list.fold(symmetries, 0)
+  case note {
+    Horizontal(n) -> 100 * n
+    Vertical(n) -> n
+  } + acc
+}
+
+fn solve(input: String, errors: Int) {
+  input
+  |> string.split("\n\n")
+  |> list.map(fn(strs) {
+    strs
+    |> string.split("\n")
+    |> list.map(string.to_graphemes)
+    |> get_symmetry_type(errors)
+  })
+  |> result.values
+  |> summarize_notes
+  |> string.inspect
+}
+
+pub fn part1(input: String) {
+  solve(input, 0)
+}
+
+pub fn part2(input: String) {
+  solve(input, 1)
+}
+
+pub fn main() {
+  let assert Ok(part) = adglent.get_part()
+  let assert Ok(input) = adglent.get_input("13")
+  case part {
+    First ->
+      part1(input)
+      |> adglent.inspect
+      |> io.println
+    Second ->
+      part2(input)
+      |> adglent.inspect
+      |> io.println
+  }
+}