solution day 8 part 1

8/solve_1.ml

@@ -16,21 +16,38 @@ let input = (fst input_info);;
 let nb_rows = (fst (snd input_info));;
 let nb_columns =(snd (snd input_info));;
 
-let encode_movement direction pos = 
+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
+           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
+             (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
+           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 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 pos_x = if (delta_x > 0) then (move_n '>' pos delta_x) else (move_n '<' pos (abs delta_x))  in
+  let final_pos = if (pos_x == -1) then -1 else (move_n '^' pos_x delta_y) in
+  final_pos
+;;
+  
+let place_antinode_down delta_x delta_y pos =
+  let pos_x = if (delta_x > 0) then (move_n '<' pos delta_x) else (move_n '>' pos (abs delta_x)) in
+  let final_pos = if (pos_x == -1) then -1 else (move_n 'v' pos_x delta_y) in
+  final_pos
+;;    
+
 let get_antennas =
     let rec aux pos accum=
     try
@@ -41,11 +58,55 @@ let get_antennas =
   aux 0 CharSet.empty
 ;;
 
-let solve = 0
+(* 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
+      if (anti_node1 != -1) then
+        (if (anti_node2 != -1) then
+          (aux (pos_antenna2) (IntSet.add anti_node1 (IntSet.add anti_node2 accum)))
+        else (aux (pos_antenna2) (IntSet.add anti_node1 accum)))
+      else
+        (if (anti_node2 != -1) then
+          (aux (pos_antenna2) (IntSet.add anti_node2 accum))
+        else
+          (aux (pos_antenna2) 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
+  IntSet.cardinal antinodes
 ;;
 
-let () = printf "Antennas : ";
-         CharSet.iter (fun a -> printf "%c " a) get_antennas;
-         printf "\n";
-printf "Total: %d\n" solve;;
-         
+let () =
+  printf "Total: %d\n" solve;;
+

README.md

@@ -49,7 +49,7 @@ replace `<part_number>` with 1 for Part 1 or 2 for Part 2
 | 5   | ✅     | ✅     |
 | 6   | ✅     | ✅     |
 | 7   | ✅     | ✅     |
-| 8   | ⬜     | ⬜     |
+| 8   | ✅     | ⬜     |
 | ... | ...    | ...    |
 | 25  | ⬜     | ⬜     |