Day 1 solutions with original utility functions

Author: renormalize

bin/day1bin.ml

@@ -1,13 +1,9 @@
-let () = Printf.printf "Solving Day 1!\n"
+let file = "day1/input.txt"
 
-let line_list = Day1.lines "day1/input.txt"
+let () =
+ Printf.printf "Solution for part 1 of day 1 is: %d\n"
+ (Day1.part1_calibration_sum file)
 
-let x = List.fold_left (+) 0 (List.map Day1.calib_value line_list)
-
-let () = Printf.printf "Part 1: sum of calibration values is: %d\n" x
-
-let line_list = Day1.lines "day1/input.txt"
-
-let y = List.fold_left (+) 0 (List.map Day1.find_vals line_list)
-
-let () = Printf.printf "Part 2: sum of calibration values is: %d\n" y
+let () =
+ Printf.printf "Solution for part 2 of day 1 is: %d\n"
+ (Day1.part2_calibration_sum file)

day1/day1.ml

@@ -1,23 +1,21 @@
-(* Read the lines of the file into a string list*)
-let lines name = In_channel.input_lines (open_in name)
-let is_digit d = d >= '0' && d <= '9'
+(* read_lines reads each line in the file into a string list*)
+let read_lines file = In_channel.input_lines (In_channel.open_text file)
+let first_digit line = line.[Str.search_forward (Str.regexp "[0-9]") line 0]
+
+let last_digit line =
+ line.[Str.search_backward (Str.regexp "[0-9]") line (String.length line - 1)]
+
+let is_digit c = Char.code c >= Char.code '0' && Char.code c <= Char.code '9'
 let to_digit c = Char.code c - Char.code '0'
 
-(* First digit and last digit *)
-let fst_lst s =
- let rec first_digit s i =
- if is_digit s.[i] then s.[i] else first_digit s (i + 1)
+let part1_calibration_sum file =
+ let calibration_value line =
+ (10 * to_digit (first_digit line)) + to_digit (last_digit line)
  in
- let rec last_digit s i =
- if is_digit s.[i] then s.[i] else last_digit s (i - 1)
- in
- (first_digit s 0, last_digit s (String.length s - 1))
-
-let calib_value s =
- let fst, lst = fst_lst s in
- (10 * to_digit fst) + to_digit lst
+ let calibration_list file = List.map calibration_value (read_lines file) in
+ List.fold_left ( + ) 0 (calibration_list file)
 
-let digit_words =
+let word_to_digit =
  [
  ("zero", 0);
  ("one", 1);
@@ -31,26 +29,42 @@ let digit_words =
  ("nine", 9);
  ]
 
-(* iterate through the string character by character and find the possible numbers*)
+let rec check_start line word_map i =
+ match word_map with
+ | [] -> None
+ | h :: t ->
+ if
+ String.starts_with ~prefix:(fst h)
+ (String.sub line i (String.length line - i))
+ then Some (snd h)
+ else check_start line t i
 
-let substr s i = String.sub s i (String.length s - i)
+let rec check_end line word_map i =
+ match word_map with
+ | [] -> None
+ | h :: t ->
+ if String.ends_with ~suffix:(fst h) (String.sub line 0 (i + 1)) then
+ Some (snd h)
+ else check_end line t i
 
-let string_begins_with s i =
- List.find_map
- (fun (word, value) ->
- if String.starts_with ~prefix:word (substr s i) then Some value else None)
- digit_words
+let rec parse_first_digit line i =
+ if is_digit line.[i] then to_digit line.[i]
+ else
+ match check_start line word_to_digit i with
+ | None -> parse_first_digit line (i + 1)
+ | Some a -> a
 
-let match_digit s i =
- if is_digit s.[i] then Some (to_digit s.[i]) else string_begins_with s i
+let rec parse_last_digit line i =
+ if is_digit line.[i] then to_digit line.[i]
+ else
+ match check_end line word_to_digit i with
+ | None -> parse_last_digit line (i - 1)
+ | Some a -> a
 
-let find_vals line =
- let rec first i =
- match match_digit line i with Some digit -> digit | None -> first (i + 1)
- in
- let rec last i =
- match match_digit line i with Some digit -> digit | None -> last (i - 1)
- in
- let first_digit = first 0 in
- let last_digit = last (String.length line - 1) in
- (first_digit * 10) + last_digit
+let vals line =
+ (parse_first_digit line 0, parse_last_digit line (String.length line - 1))
+
+let part2_calibration_sum file =
+ let calibration_value line = (10 * fst (vals line)) + snd (vals line) in
+ let calibration_list file = List.map calibration_value (read_lines file) in
+ List.fold_left ( + ) 0 (calibration_list file)

day1/dune

@@ -1,2 +1,3 @@
 (library
- (name day1))
+ (name day1)
+ (libraries str))