From d837d1cc265e5cea16b43376ee5ced6b98b168fb Mon Sep 17 00:00:00 2001
From: Jordan Doyle <jordan@doyle.la>
Date: Wed, 25 Dec 2024 11:15:34 +0700
Subject: [PATCH] Add 2024 day 12

---
 README     |  4 ++--
 flake.lock | 24 ++++++++++++++----------
 2024/12.ml | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+), 14 deletions(-)

diff --git a/README b/README
index 0a04c45..68097cf 100644
--- a/README
+++ a/README
@@ -25,8 +25,8 @@
 |        9 | OCaml    | |        9 | Haskell  |
 |       10 | OCaml    | |       10 | Haskell  |
 |       11 | OCaml    | |       11 | Haskell  |
-+---------------------+ |       12 | Rust     |
-                        |       13 | Haskell  |
+|       12 | OCaml    | |       12 | Rust     |
++---------------------+ |       13 | Haskell  |
                         |       14 | Haskell  |
                         |       15 | Haskell  |
                         |       16 | Haskell  |
diff --git a/flake.lock b/flake.lock
index 2d33bfa..beab0ef 100644
--- a/flake.lock
+++ a/flake.lock
@@ -72,11 +72,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1733392399,
-        "narHash": "sha256-kEsTJTUQfQFIJOcLYFt/RvNxIK653ZkTBIs4DG+cBns=",
+        "lastModified": 1734649271,
+        "narHash": "sha256-4EVBRhOjMDuGtMaofAIqzJbg4Ql7Ai0PSeuVZTHjyKQ=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "d0797a04b81caeae77bcff10a9dde78bc17f5661",
+        "rev": "d70bd19e0a38ad4790d3913bf08fcbfc9eeca507",
         "type": "github"
       },
       "original": {
@@ -123,11 +123,11 @@
     },
     "nixpkgs_4": {
       "locked": {
-        "lastModified": 1733229606,
-        "narHash": "sha256-FLYY5M0rpa5C2QAE3CKLYAM6TwbKicdRK6qNrSHlNrE=",
+        "lastModified": 1733097829,
+        "narHash": "sha256-9hbb1rqGelllb4kVUCZ307G2k3/UhmA8PPGBoyuWaSw=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "566e53c2ad750c84f6d31f9ccb9d00f823165550",
+        "rev": "2c15aa59df0017ca140d9ba302412298ab4bf22a",
         "type": "github"
       },
       "original": {
@@ -145,11 +145,11 @@
         "nixpkgs": "nixpkgs_2"
       },
       "locked": {
-        "lastModified": 1733424534,
-        "narHash": "sha256-yNH0n8C0JyGVnoXeFdSHJTXzEBPyxx1jPu7ez1vbNVg=",
+        "lastModified": 1734619130,
+        "narHash": "sha256-aibxngbQH4iGvq71ajf393u3BdhMhkrW1RdOj5NiaWA=",
         "owner": "ocaml",
         "repo": "ocaml-lsp",
-        "rev": "93d9d6554fc127d475c4c27d878552c88d92d43d",
+        "rev": "1628871bc216c708803376b83d2f4de05cafe4c0",
         "type": "github"
       },
       "original": {
@@ -215,11 +215,11 @@
         "nixpkgs": "nixpkgs_4"
       },
       "locked": {
-        "lastModified": 1733440889,
-        "narHash": "sha256-qKL3vjO+IXFQ0nTinFDqNq/sbbnnS5bMI1y0xX215fU=",
+        "lastModified": 1734982074,
+        "narHash": "sha256-N7M37KP7cHWoXicuE536GrVvU8nMDT/gpI1kja2hkdg=",
         "owner": "numtide",
         "repo": "treefmt-nix",
-        "rev": "50862ba6a8a0255b87377b9d2d4565e96f29b410",
+        "rev": "e41e948cf097cbf96ba4dff47a30ea6891af9f33",
         "type": "github"
       },
       "original": {
diff --git a/2024/12.ml b/2024/12.ml
new file mode 100755
index 0000000..33baf80 100755
--- /dev/null
+++ a/2024/12.ml
@@ -1,0 +1,87 @@
+#!/usr/bin/env nix-shell
+
+(*
+#!nix-shell --pure -i ocaml -p ocaml
+*)
+
+let input =
+  let rec aux () =
+    try
+      let parsed_line = read_line () |> String.to_seq |> List.of_seq in
+      parsed_line :: aux ()
+    with End_of_file -> []
+  in
+  aux () |> List.filter (fun v -> List.length v > 0)
+
+let input' = input |> List.map Array.of_list |> Array.of_list
+
+let is_valid (x, y) =
+  x >= 0 && y >= 0 && y < Array.length input' && x < Array.length input'.(0)
+
+let points =
+  let rec walk_matching c x y visited =
+    if (not (List.mem (x, y) visited)) && is_valid (x, y) && input'.(y).(x) == c
+    then
+      (x, y) :: visited
+      |> walk_matching c (x - 1) y
+      |> walk_matching c (x + 1) y
+      |> walk_matching c x (y + 1)
+      |> walk_matching c x (y - 1)
+    else visited
+  in
+  let rec aux x y visited = function
+    | [] ->
+        []
+    | [] :: rows ->
+        aux 0 (y + 1) visited rows
+    | (c :: cols) :: rows ->
+        if List.mem (x, y) visited then aux (x + 1) y visited (cols :: rows)
+        else
+          let matching = walk_matching c x y [] in
+          matching :: aux (x + 1) y (matching @ visited) (cols :: rows)
+  in
+  aux 0 0 [] input
+
+let has_neighbour points (x, y) (dx, dy) =
+  let neighbour = (x + dx, y + dy) in
+  List.exists (( = ) neighbour) points
+
+let fetch_neighbours points (x, y) =
+  [(0, 1); (1, 0); (0, -1); (-1, 0)]
+  |> List.filter (has_neighbour points (x, y))
+
+let count_shared_edges points =
+  List.fold_left
+    (fun acc (x, y) -> acc + (fetch_neighbours points (x, y) |> List.length))
+    0 points
+
+let count_corners points =
+  let is_corner (x, y) ((dy1, dx1), (dy2, dx2)) =
+    let left_match = has_neighbour points (x, y) (dx1, dy1) in
+    let right_match = has_neighbour points (x, y) (dx2, dy2) in
+    let mid_match = has_neighbour points (x, y) (dx1 + dx2, dy1 + dy2) in
+    ((not left_match) && not right_match)
+    || (left_match && right_match && not mid_match)
+  in
+  let count_corners (x, y) =
+    [((0, -1), (1, 0)); ((1, 0), (0, 1)); ((0, 1), (-1, 0)); ((-1, 0), (0, -1))]
+    |> List.filter (is_corner (x, y))
+    |> List.length
+  in
+  List.fold_left (fun acc (x, y) -> acc + count_corners (x, y)) 0 points
+
+let part1 =
+  let calc points =
+    let area = List.length points in
+    let perimeter = (4 * area) - count_shared_edges points in
+    area * perimeter
+  in
+  points |> List.map calc |> List.fold_left ( + ) 0
+
+let _ = part1 |> print_int |> print_newline
+
+let part2 =
+  let calc points = List.length points * count_corners points in
+  points |> List.map calc |> List.fold_left ( + ) 0
+
+let _ = part2 |> print_int |> print_newline
--
rgit 0.1.5