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1 files changed, 81 insertions, 0 deletions

diff --git a/gleam/aoc2019/src/aoc_2019/day_2.gleam b/gleam/aoc2019/src/aoc_2019/day_2.gleam
new file mode 100644
index 0000000..8faa0ea
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+++ b/gleam/aoc2019/src/aoc_2019/day_2.gleam
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+import gary.{type ErlangArray}
+import gary/array.{type ArrayError}
+import gleam/bool
+import gleam/int
+import gleam/list
+import gleam/result
+import gleam/string
+
+pub fn parse(input: String) -> ErlangArray(Int) {
+  input
+  |> string.split(",")
+  |> list.map(int.parse)
+  |> result.values()
+  |> array.from_list(default: -1)
+  |> array.make_fixed()
+}
+
+pub fn pt_1(input: ErlangArray(Int)) -> Int {
+  let assert Ok(result) =
+    input
+    |> edit_starting_intcodes(12, 2)
+    |> run_intcode(0)
+
+  result
+}
+
+pub fn pt_2(input: ErlangArray(Int)) -> Int {
+  let assert [result] = {
+    use noun <- list.flat_map(list.range(0, 99))
+    use verb <- list.filter_map(list.range(0, 99))
+    let result = input |> edit_starting_intcodes(noun, verb) |> run_intcode(0)
+    case result == Ok(19_690_720) {
+      True -> Ok(100 * noun + verb)
+      False -> Error(Nil)
+    }
+  }
+
+  result
+}
+
+fn run_intcode(
+  intcode: ErlangArray(Int),
+  pointer: Int,
+) -> Result(Int, ArrayError) {
+  let assert Ok(op_code) = array.get(intcode, pointer)
+  let op = get_op(op_code)
+
+  use <- bool.guard(result.is_error(op), array.get(intcode, 0))
+  let assert Ok(position_1) = array.get(intcode, pointer + 1)
+  let assert Ok(position_2) = array.get(intcode, pointer + 2)
+  let assert Ok(position_3) = array.get(intcode, pointer + 3)
+
+  let assert Ok(value_1) = array.get(intcode, position_1)
+  let assert Ok(value_2) = array.get(intcode, position_2)
+
+  let assert Ok(f) = op
+  let new_value = f(value_1, value_2)
+  let assert Ok(updated_intcode) = array.set(intcode, position_3, new_value)
+  run_intcode(updated_intcode, pointer + 4)
+}
+
+fn edit_starting_intcodes(
+  intcodes: ErlangArray(Int),
+  new_code_1: Int,
+  new_code_2: Int,
+) -> ErlangArray(Int) {
+  let assert Ok(updated) =
+    intcodes
+    |> array.set(at: 1, put: new_code_1)
+    |> result.try(array.set(into: _, at: 2, put: new_code_2))
+  updated
+}
+
+fn get_op(code: Int) -> Result(fn(Int, Int) -> Int, Nil) {
+  case code {
+    1 -> Ok(int.add)
+    2 -> Ok(int.multiply)
+    99 -> Error(Nil)
+    _ -> panic as "bad opcode"
+  }
+}