1 files changed, 48 insertions, 0 deletions
diff --git a/aoc-2020-gleam/src/util/pos2.gleam b/aoc-2020-gleam/src/util/pos2.gleam
new file mode 100644
index 0000000..4de2ab9
--- /dev/null
+++ b/aoc-2020-gleam/src/util/pos2.gleam
@@ -0,0 +1,48 @@
+import gleam/int
+import gleam/bool
+import gleam/list
+import gleam/set.{Set}
+
+pub type Pos2 =
+  #(Int, Int)
+
+pub const zero = #(0, 0)
+
+pub fn directions8() -> Set(Pos2) {
+  set.from_list({
+    use x <- list.flat_map(over: [-1, 0, 1])
+    use y <- list.flat_map(over: [-1, 0, 1])
+    let pos = #(x, y)
+    use <- bool.guard(when: pos == zero, return: [])
+    [pos]
+  })
+}
+
+pub fn add(p1: Pos2, p2: Pos2) -> Pos2 {
+  #(p1.0 + p2.0, p1.1 + p2.1)
+}
+
+pub fn sub(p1: Pos2, p2: Pos2) -> Pos2 {
+  #(p1.0 - p2.0, p1.1 - p2.1)
+}
+
+pub fn mul(p: Pos2, by scalar: Int) -> Pos2 {
+  #(p.0 * scalar, p.1 * scalar)
+}
+
+pub fn neighbours8(p: Pos2) -> Set(Pos2) {
+  directions8()
+  |> set.to_list
+  |> list.map(with: add(p, _))
+  |> set.from_list
+}
+
+pub fn manhattan_dist(from p1: Pos2, to p2: Pos2) -> Int {
+  int.absolute_value(p1.0 - p2.0) + int.absolute_value(p1.1 - p2.1)
+}
+
+pub fn rotate_around_origin(this p: Pos2, by times: Int) -> Pos2 {
+  let assert Ok(sin) = list.at([0, -1, 0, 1], times)
+  let assert Ok(cos) = list.at([1, 0, -1, 0], times)
+  #(p.0 * cos - p.1 * sin, p.0 * sin + p.1 * cos)
+}