1 files changed, 65 insertions, 0 deletions
diff --git a/aoc2017-gleam/src/aoc_2017/day_6.gleam b/aoc2017-gleam/src/aoc_2017/day_6.gleam
new file mode 100644
index 0000000..84222e1
--- /dev/null
+++ b/aoc2017-gleam/src/aoc_2017/day_6.gleam
@@ -0,0 +1,65 @@
+import gary.{type ErlangArray}
+import gary/array
+import gleam/bool
+import gleam/int
+import gleam/list
+import gleam/result
+import gleam/set.{type Set}
+import gleam/string
+
+pub fn parse(input) -> ErlangArray(Int) {
+  input
+  |> string.split("\t")
+  |> list.map(int.parse)
+  |> result.values()
+  |> array.from_list(default: -1)
+  |> array.make_fixed()
+}
+
+pub fn pt_1(input: ErlangArray(Int)) {
+  check_cycle(input, set.from_list([input]), 1).1
+}
+
+pub fn pt_2(input: ErlangArray(Int)) {
+  let #(target, cycle) = check_cycle(input, set.from_list([input]), 1)
+  cycle - check_cycle(input, set.from_list([input, target]), 1).1
+}
+
+fn get_max(array: ErlangArray(Int)) -> #(Int, Int) {
+  use index, value, max <- array.fold(over: array, from: #(-1, -1))
+  case value > max.1 {
+    True -> #(index, value)
+    False -> max
+  }
+}
+
+fn redistribute(
+  array: ErlangArray(Int),
+  pointer: Int,
+  remaining: Int,
+) -> ErlangArray(Int) {
+  use <- bool.guard(remaining == 0, array)
+  case array.get(from: array, at: pointer) {
+    Error(_) -> redistribute(array, 0, remaining)
+    Ok(n) -> {
+      let assert Ok(updated_array) =
+        array.set(into: array, at: pointer, put: n + 1)
+      redistribute(updated_array, pointer + 1, remaining - 1)
+    }
+  }
+}
+
+fn check_cycle(
+  current: ErlangArray(Int),
+  cache: Set(ErlangArray(Int)),
+  cycle: Int,
+) -> #(ErlangArray(Int), Int) {
+  let #(index, to_redistribute) = current |> get_max
+  let assert Ok(zeroed) = array.set(into: current, at: index, put: 0)
+  let next = redistribute(zeroed, index + 1, to_redistribute)
+
+  case set.contains(cache, next) {
+    True -> #(next, cycle)
+    False -> check_cycle(next, set.insert(cache, next), cycle + 1)
+  }
+}