1 files changed, 55 insertions, 0 deletions
diff --git a/aoc2017-gleam/src/aoc_2017/day_17.gleam b/aoc2017-gleam/src/aoc_2017/day_17.gleam
new file mode 100644
index 0000000..5904cab
--- /dev/null
+++ b/aoc2017-gleam/src/aoc_2017/day_17.gleam
@@ -0,0 +1,55 @@
+import gleam/int
+import gleam/list
+import glearray
+
+pub fn parse(input: String) {
+  let assert Ok(n) = int.parse(input)
+  n
+}
+
+pub fn pt_1(input: Int) {
+  let assert [_, result] =
+    next_spin([0], 0, 1, input)
+    |> list.drop_while(fn(x) { x != 2017 })
+    |> list.take(2)
+
+  result
+}
+
+fn next_spin(list: List(Int), position: Int, cycle: Int, step: Int) {
+  case cycle {
+    2018 -> list
+    _ -> {
+      let next_position = { position + step } % cycle + 1
+      next_spin(
+        insert_at(list, next_position, cycle),
+        next_position,
+        cycle + 1,
+        step,
+      )
+    }
+  }
+}
+
+fn insert_at(xs: List(a), at index: Int, insert new: a) {
+  let #(left, right) = list.split(xs, index)
+  list.concat([left, [new], right])
+}
+
+pub fn pt_2(input: Int) {
+  next_spin_tracking_zero(0, 0, 1, input)
+}
+
+fn next_spin_tracking_zero(acc: Int, position: Int, cycle: Int, step: Int) {
+  case cycle {
+    50_000_001 -> acc
+    _ -> {
+      let next_position = { position + step } % cycle + 1
+      let next_acc = case next_position {
+        1 -> cycle
+        _ -> acc
+      }
+      next_spin_tracking_zero(next_acc, next_position, cycle + 1, step)
+    }
+  }
+}