start day 8 part 2

8/solve_2.ml

@@ -1,5 +1,7 @@
 open Stdio
-(* open Str *)
+open Str
+module CharSet = Set.Make(Char)
+module IntSet = Set.Make(Int)
 
 let input_info = 
   let rec one_string inp nb_rows nb_columns = 
@@ -10,13 +12,107 @@ let input_info =
   in one_string "" 0 0
 ;;
 
-let grid = (fst input_info);;
+let input = (fst input_info);;
 let nb_rows = (fst (snd input_info));;
 let nb_columns =(snd (snd input_info));;
 
-let solve = 0
+let encode_movement direction pos =
+  match direction with
+  | '^' -> let new_pos = pos - nb_columns in
+           if (new_pos < 0) then -1 else new_pos
+  | 'v' -> let new_pos = (pos + nb_columns) in
+           if (new_pos >= (nb_rows*nb_columns)) then -1  else new_pos
+  | '<' -> let new_pos = (pos - 1) in
+           if (new_pos mod nb_columns == nb_columns -1) then -1 else
+             (if (new_pos < 0) then -1 else new_pos)
+  | '>' -> let new_pos = (pos + 1) in
+           if (new_pos mod nb_columns == 0) then -1 else
+             (if (new_pos >= (nb_rows*nb_columns)) then -1 else new_pos)
+  | _ -> -1 (*Not supposed to happen*)
 ;;
 
-let () = printf "%d %d\n\n%s" nb_rows nb_columns grid;
-printf "Total: %d\n" solve;;
-         
+let rec move_n direction pos n =
+  if (n <= 0 || pos == -1) then pos
+  else (move_n direction (encode_movement direction pos) (n-1))
+  
+
+let place_antinode_up delta_x delta_y pos =
+  let rec aux accum p =
+    let pos_x = if (delta_x > 0) then (move_n '>' p delta_x) else (move_n '<' p (abs delta_x))  in
+    if (pos_x == -1) then accum
+    else
+    (let final_pos = (move_n '^' pos_x delta_y) in
+    if (final_pos == -1) then accum else (aux (final_pos::accum) final_pos))
+  in
+  aux [] pos
+;;
+
+let place_antinode_down delta_x delta_y pos =
+  let rec aux accum p =
+    let pos_x = if (delta_x > 0) then (move_n '<' p delta_x) else (move_n '>' p (abs delta_x))  in
+    if (pos_x == -1) then accum
+    else
+    (let final_pos = (move_n 'v' pos_x delta_y) in
+    if (final_pos == -1) then accum else (aux (final_pos::accum) final_pos))
+  in
+  aux [] pos
+;;
+
+let get_antennas =
+    let rec aux pos accum=
+    try
+      let pos_antenna = search_forward (regexp {|[^.]|}) input pos in
+      aux (pos_antenna + 1) (CharSet.add input.[pos_antenna] accum) 
+    with Not_found -> accum
+  in
+  aux 0 CharSet.empty
+;;
+
+(* Get distance between two antennas
+   requires pos1 < pos2;
+*)
+let distance pos1 pos2 =
+  let y_pos1, x_pos1 = (pos1/nb_columns, pos1 mod nb_columns) in
+  let y_pos2, x_pos2 = (pos2/nb_columns, pos2 mod nb_columns) in
+  let x_diff, y_diff = (x_pos1 - x_pos2), (y_pos2 - y_pos1) in
+  (x_diff, y_diff)
+;;
+
+
+let create_antinodes antenna fixed_antenna_pos =
+  let rec aux pos accum =
+    try
+      let pos_antenna2 = search_forward (regexp (String.make 1 antenna)) input (pos + 1) in
+      let x_diff, y_diff = (distance fixed_antenna_pos pos_antenna2) in
+      let anti_node1 = (place_antinode_up x_diff y_diff fixed_antenna_pos) in
+      let anti_node2 = (place_antinode_down x_diff y_diff pos_antenna2) in
+      let set_antinode1 = List.fold_left (fun acc p -> IntSet.add p acc) IntSet.empty anti_node1 in
+      let set_antinode2 = List.fold_left (fun acc p -> IntSet.add p acc) set_antinode1 anti_node2 in
+      aux (pos_antenna2) (IntSet.union (IntSet.union set_antinode1 set_antinode2) accum)
+    with Not_found -> accum
+  in
+  aux fixed_antenna_pos IntSet.empty
+;;
+
+let create_all_antinodes antenna =
+  let rec aux pos accum =
+  try
+    let pos = search_forward (regexp (String.make 1 antenna)) input pos in
+    let set_positions = create_antinodes antenna pos in
+    aux (pos+1) (IntSet.union accum set_positions)
+  with Not_found -> accum
+  in
+  aux 0 IntSet.empty
+;;
+
+let solve =
+  let antinodes =
+    CharSet.fold (fun c acc -> (IntSet.union (create_all_antinodes c) acc)) get_antennas IntSet.empty in
+  printf "Antinodes : \n";
+  IntSet.iter (fun d -> printf "%d " d) antinodes;
+  IntSet.cardinal antinodes
+;;
+
+let () =
+  printf "Total: %d\n" solve;;
+