Solution day 4 part 1

4/solve_1.ml

@@ -1,4 +1,5 @@
 open Stdio
+open Str
 
 let next_char = function
 | 'X' -> 'M'
@@ -7,21 +8,62 @@ let next_char = function
 | _ -> 'Z'
 ;;
 
-let nb_columns = 
-  let line = In_channel.input_line In_channel.stdin in
-  match line with 
-  | None -> 0
-  | Some x -> String.length x 
+let input_info = 
+  let rec one_string inp nb_rows nb_columns = 
+    let line = In_channel.input_line In_channel.stdin in
+    match line with
+    | None -> (inp, (nb_rows, nb_columns))
+    | Some x -> one_string (inp ^ x) (nb_rows + 1) (String.length x)
+  in one_string "" 0 0
 ;;
 
-let nb_rows =
-  let rec aux accum = 
-    let line = In_channel.input_line In_channel.stdin in
-    match line with 
-    | None -> accum
-    | Some _ -> aux (accum+1)
-  in
-  aux 1
+let input = fst input_info;;
+let nb_rows = (fst (snd input_info));;
+let nb_columns = (snd (snd input_info));;
+
+
+let get_valid_indexes letter pos = 
+  let filter i = 
+  ( let right     = (if ((pos mod nb_columns) < (nb_columns - i)) then (pos + 1) else -99) in 
+    let left      = (if ((pos mod nb_columns) > (i-1) ) then (pos -1) else -99) in
+    let up        = (if ((pos - i*nb_columns) >= 0) then (pos - nb_columns) else -99) in
+    let down      = (if ((pos + i*nb_columns) < nb_columns*nb_rows) then (pos + nb_columns) else -99) in
+    let upright   = (let is_valid_upright = ((((pos - i*(nb_columns - 1)) mod nb_columns) - (pos mod nb_columns)) == i) in
+                      if is_valid_upright then (up + 1) else -99) in
+    let upleft    = (let is_valid_upleft = (((pos mod nb_columns) - ((pos - i*(nb_columns + 1)) mod nb_columns)) == i) in
+                      if is_valid_upleft then (up - 1) else -99) in
+    let downright = (let is_valid_downright = ((((pos + i*(nb_columns + 1)) mod nb_columns) - (pos mod nb_columns)) == i) in
+                      if is_valid_downright then (down + 1) else -99) in
+    let downleft  = (let is_valid_downleft = (((pos mod nb_columns) - ((pos + i*(nb_columns - 1)) mod nb_columns)) == i) in
+                      if is_valid_downleft then (down - 1) else -99) in
+    List.filter (fun x -> (snd x) >= 0) [('r',right);('l',left);('u',up);
+                                   ('d',down);('R',upright);('L',upleft);
+                                   ('\\',downright);('/',downleft)]) in
+  (match letter with
+  | 'X'     -> filter 3
+  | 'M'     -> filter 2
+  | 'A'     -> filter 1
+  | 'S' | _ -> [])
 ;;
 
-let () =  printf "rows : %d ; columns : %d\n" nb_rows nb_columns
+let rec count_xmas letter pos direction accum= 
+  if letter == 'S' then (accum + 1) else
+  let list_indexes = get_valid_indexes letter pos in
+  let direction_filter = if direction != 'a' then List.filter (fun x -> (fst x) == direction) list_indexes else list_indexes in
+  let adjacent_wanted = List.filter (fun l -> input.[snd l] == (next_char letter)) direction_filter in
+  let rec aux = (function
+                | (d, i):: tl -> count_xmas input.[i] i d accum + aux tl
+                | [] -> accum)
+  in aux adjacent_wanted
+;;
+
+let solve = 
+  let rec aux pos accum=
+    try
+      let pos_x = search_forward (regexp "X") input pos in
+      aux (pos_x + 1) (accum + count_xmas 'X' pos_x 'a' 0 )
+    with Not_found -> accum
+  in
+    aux 0 0
+;;
+let () =  printf "Total : %d\n" solve

README.md

@@ -45,7 +45,7 @@ replace `<part_number>` with 1 for Part 1 or 2 for Part 2
 | 1   | ✅     | ✅     |
 | 2   | ✅     | ✅     |
 | 3   | ✅     | ✅     |
-| 4   | ⬜     | ⬜     |
+| 4   | ✅     | ⬜     |
 | ... | ...    | ...    |
 | 25  | ⬜     | ⬜     |