1 files changed, 104 insertions, 0 deletions
diff --git a/aoc2023-gleam/src/day15/solve.gleam b/aoc2023-gleam/src/day15/solve.gleam
new file mode 100644
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+++ b/aoc2023-gleam/src/day15/solve.gleam
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+import adglent.{First, Second}
+import gleam/io
+import gleam/string
+import gleam/list
+import gleam/int
+import gleam/dict.{type Dict}
+import gleam/option.{None, Some}
+
+fn split(input: String) -> List(String) {
+  input
+  |> string.split(",")
+}
+
+fn hash_algorithm(str: String) -> Int {
+  let codepoints =
+    str
+    |> string.to_utf_codepoints()
+    |> list.map(string.utf_codepoint_to_int)
+  use acc, c <- list.fold(codepoints, 0)
+  let assert Ok(acc) = int.modulo({ acc + c } * 17, 256)
+  acc
+}
+
+pub fn part1(input: String) -> String {
+  input
+  |> split
+  |> list.fold(0, fn(acc, str) { acc + hash_algorithm(str) })
+  |> string.inspect
+}
+
+type Instruction {
+  Remove(label: String)
+  Insert(label: String, focal: Int)
+}
+
+fn read_instruction(str: String) -> Instruction {
+  case string.split(str, "=") {
+    [label, focal_str] -> {
+      let assert Ok(focal) = int.parse(focal_str)
+      Insert(label, focal)
+    }
+    _ -> Remove(string.drop_right(str, 1))
+  }
+}
+
+fn parse_instructions(insts: List(String)) -> Dict(Int, List(#(String, Int))) {
+  use acc, inst <- list.fold(insts, dict.new())
+  case read_instruction(inst) {
+    Remove(label) -> remove_lens(acc, label)
+    Insert(label, focal) -> insert_lens(acc, label, focal)
+  }
+}
+
+fn remove_lens(boxes, label) {
+  use v <- dict.update(boxes, hash_algorithm(label))
+  case v {
+    Some(lenses) ->
+      case list.key_pop(lenses, label) {
+        Ok(#(_, updated)) -> updated
+        Error(Nil) -> lenses
+      }
+    None -> []
+  }
+}
+
+fn insert_lens(boxes, label, focal) {
+  use v <- dict.update(boxes, hash_algorithm(label))
+  case v {
+    Some(lenses) -> list.key_set(lenses, label, focal)
+    None -> [#(label, focal)]
+  }
+}
+
+fn focusing_power(boxes: Dict(Int, List(#(String, Int)))) -> Int {
+  use acc, k, v <- dict.fold(boxes, 0)
+  let box_acc = {
+    use acc, lens, i <- list.index_fold(v, 0)
+    acc + lens.1 * { i + 1 }
+  }
+  acc + { k + 1 } * box_acc
+}
+
+pub fn part2(input: String) -> String {
+  input
+  |> split
+  |> parse_instructions
+  |> focusing_power
+  |> string.inspect
+}
+
+pub fn main() {
+  let assert Ok(part) = adglent.get_part()
+  let assert Ok(input) = adglent.get_input("15")
+  case part {
+    First ->
+      part1(input)
+      |> adglent.inspect
+      |> io.println
+    Second ->
+      part2(input)
+      |> adglent.inspect
+      |> io.println
+  }
+}