test: fix ocaml tests 2024 {WIP}HEADmain

18 files changed, 633 insertions, 1 deletions

diff --git a/ocaml/README.md b/ocaml/README.md
index 7d64eb8..a2a6b4f 100644
--- a/ocaml/README.md
+++ b/ocaml/README.md
@@ -1 +1,21 @@
 # Advent of Code: OCaml
+
+## Getting Started
+
+### How to Build
+
+```sh
+task build
+```
+
+### How to Run
+
+```sh
+task run
+```
+
+### How to Test
+
+```sh
+task test
+```
diff --git a/ocaml/flake.nix b/ocaml/flake.nix
index 0176014..7b267a1 100644
--- a/ocaml/flake.nix
+++ b/ocaml/flake.nix
@@ -39,6 +39,7 @@
             cmdliner # command line library
             ppx_deriving # derivers
             logs # logging library
+            menhir # parsing library
           ];
           sysTools = with pkgs; [
             go-task
@@ -48,4 +49,4 @@
           buildInputs = ocamlPackages ++ sysTools;
         };
     };
-}
+}
\ No newline at end of file
diff --git a/ocaml/lib/year2024/day01/part01.ml b/ocaml/lib/year2024/day01/part01.ml
new file mode 100644
index 0000000..100b12a
--- /dev/null
+++ b/ocaml/lib/year2024/day01/part01.ml
@@ -0,0 +1,40 @@
+(* Day 1: Part 1 *)
+
+let calculate_distance x y = Stdlib.abs (x - y)
+
+(** Require: left and right to be the same length *)
+let solve left right =
+  let sorted_left = List.sort Stdlib.compare left in
+  let sorted_right = List.sort Stdlib.compare right in
+  let distances = List.map2 calculate_distance sorted_left sorted_right in
+  List.fold_left ( + ) 0 distances
+
+let left line =
+  let pos = 0 in
+  let len = String.index line ' ' in
+  String.sub line pos len
+
+let right line =
+  let pos = String.rindex line ' ' + 1 in
+  let len = String.length line - pos in
+  String.sub line pos len
+
+let line_to_tuple line = (left line, right line)
+
+let lines_to_lists lines =
+  let tuples = List.map line_to_tuple lines in
+  let left =
+    List.map
+      (fun t ->
+        let l, _ = t in
+        int_of_string l)
+      tuples
+  in
+  let right =
+    List.map
+      (fun t ->
+        let _, r = t in
+        int_of_string r)
+      tuples
+  in
+  (left, right)
diff --git a/ocaml/lib/year2024/day01/part02.ml b/ocaml/lib/year2024/day01/part02.ml
new file mode 100644
index 0000000..25c8b7d
--- /dev/null
+++ b/ocaml/lib/year2024/day01/part02.ml
@@ -0,0 +1,44 @@
+(* Day 1: Part 2 *)
+
+let rec count_occurrances_help element acc lst =
+  match lst with
+  | [] -> acc
+  | h :: t ->
+      if h = element then count_occurrances_help element (acc + 1) t
+      else count_occurrances_help element acc t
+
+let count_occurrances element lst = count_occurrances_help element 0 lst
+
+let solve left right =
+  List.map (fun x -> x * count_occurrances x right) left
+  |> List.fold_left ( + ) 0
+
+let left line =
+  let pos = 0 in
+  let len = String.index line ' ' in
+  String.sub line pos len
+
+let right line =
+  let pos = String.rindex line ' ' + 1 in
+  let len = String.length line - pos in
+  String.sub line pos len
+
+let line_to_tuple line = (left line, right line)
+
+let lines_to_lists lines =
+  let tuples = List.map line_to_tuple lines in
+  let left =
+    List.map
+      (fun t ->
+        let l, _ = t in
+        int_of_string l)
+      tuples
+  in
+  let right =
+    List.map
+      (fun t ->
+        let _, r = t in
+        int_of_string r)
+      tuples
+  in
+  (left, right)
diff --git a/ocaml/lib/year2024/day02/part01.ml b/ocaml/lib/year2024/day02/part01.ml
new file mode 100644
index 0000000..32d7ab8
--- /dev/null
+++ b/ocaml/lib/year2024/day02/part01.ml
@@ -0,0 +1,42 @@
+(* Day 2: Part 1 *)
+
+type level = int
+type reports = level list list
+
+let rec compare_report_levels_helper comparison prev report =
+  match report with
+  | [] -> true
+  | h :: t -> comparison prev h && compare_report_levels_helper comparison h t
+
+let compare_report_levels comparison report =
+  match report with
+  | [] -> true
+  | h :: t -> compare_report_levels_helper comparison h t
+
+let all_increasing report = compare_report_levels ( < ) report
+let all_decreasing report = compare_report_levels ( > ) report
+
+let at_least_one report =
+  compare_report_levels (fun prev curr -> prev <> curr) report
+
+let at_most_three report =
+  compare_report_levels (fun prev curr -> abs (prev - curr) <= 3) report
+
+let check_report_safety report =
+  if not (all_increasing report || all_decreasing report) then false
+  else if not (at_least_one report && at_most_three report) then false
+  else true
+
+let rec count_safe_reports acc lst =
+  match lst with
+  | [] -> acc
+  | h :: t ->
+      if h then count_safe_reports (acc + 1) t else count_safe_reports acc t
+
+let solve reports =
+  reports |> List.map check_report_safety |> count_safe_reports 0
+
+let line_to_report line =
+  line |> String.split_on_char ' ' |> List.map int_of_string
+
+let lines_to_reports lines = List.map line_to_report lines
diff --git a/ocaml/lib/year2024/day03/part01.ml b/ocaml/lib/year2024/day03/part01.ml
new file mode 100644
index 0000000..c12b68a
--- /dev/null
+++ b/ocaml/lib/year2024/day03/part01.ml
@@ -0,0 +1,33 @@
+(* Day 3: Part 1 *)
+
+let find_mul text =
+  let regex_or_err = Re2.create "mul\\(([0-9]{1,3}),([0-9]{1,3})\\)" in
+  match regex_or_err with
+  | Ok regex -> (
+      let matches = Re2.get_matches regex text in
+      match matches with Ok matches -> matches | Error _ -> [])
+  | Error _ -> []
+
+let extract_pairs (matches : Re2.Match.t list) : (int * int) list =
+  List.map
+    (fun x ->
+      let left = Re2.Match.get x ~sub:(`Index 1) in
+      match left with
+      | None -> (0, 0)
+      | Some left -> (
+          let left_num = int_of_string left in
+          let right = Re2.Match.get x ~sub:(`Index 2) in
+          match right with
+          | None -> (0, 0)
+          | Some right ->
+              let right_num = int_of_string right in
+              (left_num, right_num)))
+    matches
+
+let solve input =
+  input |> find_mul |> extract_pairs
+  |> List.fold_left
+       (fun acc pair ->
+         let left, right = pair in
+         acc + (left * right))
+       0
diff --git a/ocaml/lib/year2024/day04/part01.ml b/ocaml/lib/year2024/day04/part01.ml
new file mode 100644
index 0000000..acb3e3b
--- /dev/null
+++ b/ocaml/lib/year2024/day04/part01.ml
@@ -0,0 +1,85 @@
+(* Day 4: Part 1 *)
+
+type character = { index : int; character : char }
+type direction = N | NE | E | SE | S | SW | W | NW
+
+let all_directions = [ N; NE; E; SE; S; SW; W; NW ]
+let needle = "XMAS"
+
+(** [calculate_row_offset lines] is the offset used to move between the rows of
+    the concatenated variant of [lines] as though it were a grid. Requires:
+    values of [lines] all have the same length *)
+let calculate_row_offset lines =
+  match lines with [] -> 0 | h :: _ -> String.length h
+
+let join_lines lines =
+  let concat_trim acc line = acc ^ String.trim line in
+  List.fold_left concat_trim "" lines
+
+let explode s = List.init (String.length s) (String.get s)
+let is_in_bounds length index = index >= 0 && index < length
+
+let get_at_index line index =
+  let length = String.length line in
+  if not (is_in_bounds length index) then "."
+  else
+    let character = String.get line index in
+    Char.escaped character
+
+let get_direction_index row_offset direction index =
+  match direction with
+  | N -> index - row_offset
+  | NE -> index - row_offset + 1
+  | E -> index + 1
+  | SE -> index + row_offset + 1
+  | S -> index + row_offset
+  | SW -> index + row_offset - 1
+  | W -> index - 1
+  | NW -> index - row_offset - 1
+
+let get_direction_string get_char get_offset_index index =
+  let first = get_char index in
+  let second_index = get_offset_index index in
+  let second = get_char second_index in
+  let third_index = get_offset_index second_index in
+  let third = get_char third_index in
+  let fourth_index = get_offset_index third_index in
+  let fourth = get_char fourth_index in
+  first ^ second ^ third ^ fourth
+
+let check_direction get_from_line get_offset_index index direction =
+  get_direction_string get_from_line (get_offset_index direction) index = needle
+
+let calculate_num_of_matches line row_offset character =
+  let get_from_line_at_index = get_at_index line in
+  let get_offset_direction_index = get_direction_index row_offset in
+  let check_direction_from_index =
+    check_direction get_from_line_at_index get_offset_direction_index
+      character.index
+  in
+  all_directions
+  |> List.map check_direction_from_index
+  |> List.map (fun x -> match x with true -> 1 | false -> 0)
+  |> List.fold_left ( + ) 0
+
+(* Tried:
+   2544 -> too high
+   1272 (previous halved) -> too low *)
+let solve lines =
+  let row_offset = calculate_row_offset lines in
+  let line = join_lines lines in
+  let chars = explode line in
+  let characters = List.mapi (fun i c -> { index = i; character = c }) chars in
+  let xs =
+    List.filter
+      (fun c -> match c.character with 'X' -> true | _ -> false)
+      characters
+  in
+  let calculate_num_of_surrounding_matches_in_line =
+    calculate_num_of_matches line row_offset
+  in
+  let num_of_matches =
+    List.map calculate_num_of_surrounding_matches_in_line xs
+    |> List.fold_left ( + ) 0
+  in
+  num_of_matches
diff --git a/ocaml/lib/year2024/day05/part01.ml b/ocaml/lib/year2024/day05/part01.ml
new file mode 100644
index 0000000..96ff486
--- /dev/null
+++ b/ocaml/lib/year2024/day05/part01.ml
@@ -0,0 +1,64 @@
+(* Day 5: Part 1 *)
+
+module StringMap = Map.Make (String)
+
+let inverse_page_rule page_rule =
+  String.split_on_char '|' page_rule
+  |> fun lst ->
+  match lst with [] -> "" | _ :: _ -> String.concat "|" (List.rev lst)
+
+(** [parse_aux acc page_rules] is a map of all invalid transitions as defined by
+    [page_rules] *)
+let rec get_invalid_transitions_aux acc page_rules : unit StringMap.t =
+  match page_rules with
+  | [] ->
+      acc
+  | h :: t ->
+      get_invalid_transitions_aux
+        (acc |> StringMap.add (inverse_page_rule h) ())
+        t
+
+let get_invalid_transitions page_rules =
+  get_invalid_transitions_aux StringMap.empty page_rules
+
+(** [solve page_rules updates] is the solution for this puzzle, given the
+    [page_rules] and a list of [updates].
+
+    BELOW DOESN'T WORK: no guarantee that second page comes immediately after
+    the first
+    - pass in updates to solve
+    - make sliding window of 2 elements
+    - invert element order and concat
+    - check if key is in map from [parse page_rules],
+    - if yes, then it is an illegal transition
+    - if no, then add the list to a list for further processing *)
+let solve page_rules _ =
+  let[@warning "-26"] invalid_transitions =
+    get_invalid_transitions page_rules
+  in
+  ()
+
+let _ =
+  solve
+    [ "47|53"
+    ; "97|13"
+    ; "97|61"
+    ; "97|47"
+    ; "75|29"
+    ; "61|13"
+    ; "75|53"
+    ; "29|13"
+    ; "97|29"
+    ; "53|29"
+    ; "61|53"
+    ; "97|53"
+    ; "61|29"
+    ; "47|13"
+    ; "75|47"
+    ; "97|75"
+    ; "47|61"
+    ; "75|61"
+    ; "47|29"
+    ; "75|13"
+    ; "53|13" ]
+    []
diff --git a/ocaml/lib/year2024/dune b/ocaml/lib/year2024/dune
new file mode 100644
index 0000000..63bf2a1
--- /dev/null
+++ b/ocaml/lib/year2024/dune
@@ -0,0 +1,5 @@
+(include_subdirs qualified)
+
+(library
+ (name year2024)
+ (libraries re2))
diff --git a/ocaml/test/year2024/day01/dune b/ocaml/test/year2024/day01/dune
new file mode 100644
index 0000000..8891ccf
--- /dev/null
+++ b/ocaml/test/year2024/day01/dune
@@ -0,0 +1,11 @@
+(tests
+ (names
+   test_part01
+   test_part02)
+ (libraries
+   year2024
+   alcotest
+   qcheck-core
+   qcheck-alcotest)
+ (action (run %{test} -e))
+ (modes byte exe))
diff --git a/ocaml/test/year2024/day01/test_part01.ml b/ocaml/test/year2024/day01/test_part01.ml
new file mode 100644
index 0000000..706284d
--- /dev/null
+++ b/ocaml/test/year2024/day01/test_part01.ml
@@ -0,0 +1,30 @@
+open Year2024.Day01.Part01
+
+let test_solve haveLeft haveRight want () =
+  Alcotest.(check int) "incorrect solution" want @@ solve haveLeft haveRight
+
+let test_distance_calculation haveX haveY want () =
+  Alcotest.(check int) "incorrect solution" want
+  @@ calculate_distance haveX haveY
+
+let () =
+  let open Alcotest in
+  run "test suite for day 01 part 01"
+    [ ( "test solutions"
+      , [ test_case "empty list is 0" `Quick @@ (test_solve [] []) 0
+        ; test_case "distance between 0 and 1 is 1" `Quick
+          @@ (test_solve [0] [1]) 1
+        ; test_case "distance between 1 and 0 is 1" `Quick
+          @@ (test_solve [1] [0]) 1
+        ; test_case "smallest are paired, then next smallest, ..." `Quick
+          @@ (test_solve [1; 2; 3] [3; 2; 1]) 0
+        ; test_case "solves example correctly" `Quick
+          @@ (test_solve [3; 4; 2; 1; 3; 3] [4; 3; 5; 3; 9; 3]) 11
+        ; test_case "same number is 0 distance apart" `Quick
+          @@ (test_distance_calculation 0 0) 0
+        ; test_case "same number is 0 distance apart" `Quick
+          @@ (test_distance_calculation 1 1) 0
+        ; test_case "distance is equal to abs(x - y)" `Quick
+          @@ (test_distance_calculation 0 1) 1
+        ; test_case "order of inputs doesn't matter" `Quick
+          @@ (test_distance_calculation 1 0) 1 ] ) ]
diff --git a/ocaml/test/year2024/day01/test_part02.ml b/ocaml/test/year2024/day01/test_part02.ml
new file mode 100644
index 0000000..142add6
--- /dev/null
+++ b/ocaml/test/year2024/day01/test_part02.ml
@@ -0,0 +1,16 @@
+open Year2024.Day01.Part02
+
+let test_solve haveLeft haveRight want () =
+  Alcotest.(check int) "incorrect solution" want @@ solve haveLeft haveRight
+
+let () =
+  let open Alcotest in
+  run "test suite for day 01 part 02"
+    [ ( "test solutions"
+      , [ test_case "empty list is 0" `Quick @@ (test_solve [] []) 0
+        ; test_case "ten x zero occurrances of ten" `Quick
+          @@ (test_solve [10] [1; 2; 3]) 0
+        ; test_case "two x three occurrances of two" `Quick
+          @@ (test_solve [2] [2; 2; 2]) 6
+        ; test_case "solves example correctly" `Quick
+          @@ (test_solve [3; 4; 2; 1; 3; 3] [4; 3; 5; 3; 9; 3]) 31 ] ) ]
diff --git a/ocaml/test/year2024/day02/dune b/ocaml/test/year2024/day02/dune
new file mode 100644
index 0000000..c4a75c4
--- /dev/null
+++ b/ocaml/test/year2024/day02/dune
@@ -0,0 +1,10 @@
+(tests
+ (names
+   test_part01)
+ (libraries
+   year2024
+   alcotest
+   qcheck-core
+   qcheck-alcotest)
+ (action (run %{test} -e))
+ (modes byte exe))
diff --git a/ocaml/test/year2024/day02/test_part01.ml b/ocaml/test/year2024/day02/test_part01.ml
new file mode 100644
index 0000000..4feea41
--- /dev/null
+++ b/ocaml/test/year2024/day02/test_part01.ml
@@ -0,0 +1,41 @@
+open Year2024.Day02.Part01
+
+let test_solve have want () =
+  Alcotest.(check int) "incorrect solution" want @@ solve have
+
+let test_report_safety_check have want () =
+  Alcotest.(check bool) "incorrect report safety" want
+  @@ check_report_safety have
+
+let () =
+  let open Alcotest in
+  run "test suite for day 2 part 1"
+    [ ( "test solutions"
+      , [ test_case "empty list should have no valid reports" `Quick
+          @@ test_solve [] 0
+        ; test_case "valid report should count as one" `Quick
+          @@ test_solve [[7; 6; 4; 2; 1]] 1
+        ; test_case "provided example" `Quick
+          @@ test_solve
+               [ [7; 6; 4; 2; 1]
+               ; [1; 2; 7; 8; 9]
+               ; [9; 7; 6; 2; 1]
+               ; [1; 3; 2; 4; 5]
+               ; [8; 6; 4; 4; 1]
+               ; [1; 3; 6; 7; 9] ]
+               2 ] )
+    ; ( "test report safety check"
+      , [ test_case "all increasing" `Quick
+          @@ test_report_safety_check [1; 2; 3] true
+        ; test_case "all decreasing" `Quick
+          @@ test_report_safety_check [3; 2; 1] true
+        ; test_case "increasing and decreasing" `Quick
+          @@ test_report_safety_check [1; 3; 2] false
+        ; test_case "change of at least one" `Quick
+          @@ test_report_safety_check [1; 2; 3] true
+        ; test_case "no change" `Quick
+          @@ test_report_safety_check [1; 1; 2] false
+        ; test_case "change of at most three" `Quick
+          @@ test_report_safety_check [1; 2; 4; 7] true
+        ; test_case "change of at more than three" `Quick
+          @@ test_report_safety_check [1; 5] false ] ) ]
diff --git a/ocaml/test/year2024/day03/dune b/ocaml/test/year2024/day03/dune
new file mode 100644
index 0000000..c4a75c4
--- /dev/null
+++ b/ocaml/test/year2024/day03/dune
@@ -0,0 +1,10 @@
+(tests
+ (names
+   test_part01)
+ (libraries
+   year2024
+   alcotest
+   qcheck-core
+   qcheck-alcotest)
+ (action (run %{test} -e))
+ (modes byte exe))
diff --git a/ocaml/test/year2024/day03/test_part01.ml b/ocaml/test/year2024/day03/test_part01.ml
new file mode 100644
index 0000000..78d04e2
--- /dev/null
+++ b/ocaml/test/year2024/day03/test_part01.ml
@@ -0,0 +1,29 @@
+open Year2024.Day03.Part01
+
+let example_input =
+  "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))"
+
+let test_find_mul () =
+  Alcotest.(check (list string))
+    "incorrect mul list found"
+    ["mul(2,4)"; "mul(5,5)"; "mul(11,8)"; "mul(8,5)"]
+    (let result = find_mul example_input in
+     List.map (fun x -> Re2.Match.get_exn x ~sub:(`Index 0)) result )
+
+let test_extract_pairs () =
+  Alcotest.(check (list (pair int int)))
+    "incorrect pairs"
+    [(2, 4); (5, 5); (11, 8); (8, 5)]
+    (let matches = find_mul example_input in
+     extract_pairs matches )
+
+let test_solve () = Alcotest.(check int) "" 161 @@ solve example_input
+
+let () =
+  let open Alcotest in
+  run "test suite for day 3 part 1"
+    [ ( "test implementation"
+      , [ test_case "muls extracted from example correctly" `Quick
+          @@ test_find_mul
+        ; test_case "pairs extracted from matches" `Quick @@ test_extract_pairs
+        ; test_case "example correctly solved" `Quick @@ test_solve ] ) ]
diff --git a/ocaml/test/year2024/day04/dune b/ocaml/test/year2024/day04/dune
new file mode 100644
index 0000000..c4a75c4
--- /dev/null
+++ b/ocaml/test/year2024/day04/dune
@@ -0,0 +1,10 @@
+(tests
+ (names
+   test_part01)
+ (libraries
+   year2024
+   alcotest
+   qcheck-core
+   qcheck-alcotest)
+ (action (run %{test} -e))
+ (modes byte exe))
diff --git a/ocaml/test/year2024/day04/test_part01.ml b/ocaml/test/year2024/day04/test_part01.ml
new file mode 100644
index 0000000..5776e49
--- /dev/null
+++ b/ocaml/test/year2024/day04/test_part01.ml
@@ -0,0 +1,141 @@
+open Year2024.Day04.Part01
+
+let example_input =
+  [ "MMMSXXMASM"
+  ; "MSAMXMSMSA"
+  ; "AMXSXMAAMM"
+  ; "MSAMASMSMX"
+  ; "XMASAMXAMM"
+  ; "XXAMMXXAMA"
+  ; "SMSMSASXSS"
+  ; "SAXAMASAAA"
+  ; "MAMMMXMMMM"
+  ; "MXMXAXMASX" ]
+
+let is_in_bounds_tests =
+  let test_is_in_bounds expected length index _ =
+    let actual = is_in_bounds length index in
+    assert_equal ~printer:string_of_bool expected actual
+  in
+  [ "not in bounds if below 0" >:: test_is_in_bounds false 1 (-1)
+  ; "in bounds if gte 0 and lt length" >:: test_is_in_bounds true 1 0
+  ; "not in bounds if eq length" >:: test_is_in_bounds false 1 1
+  ; "not in bounds if gt length" >:: test_is_in_bounds false 1 2 ]
+
+let calculate_num_of_matches_tests =
+  let test_calculate_num_of_matches expected line row_offset character _ =
+    let actual = calculate_num_of_matches line row_offset character in
+    assert_equal ~printer:string_of_int expected actual
+  in
+  [ "is 0 when no matches present"
+    >:: test_calculate_num_of_matches 0 "SMMX" 1 {index= 3; character= 'X'}
+  ; "is 1 when only one match present - top to bottom"
+    >::
+    (*
+      |.|X|.|
+      |.|M|.|
+      |.|A|.|
+      |.|S|.|
+    *)
+    test_calculate_num_of_matches 1 ".X..M..A..S." 3 {index= 1; character= 'X'}
+  ; "is 1 when only one match present - top to bottom edge"
+    >::
+    (*
+      |X|.|.|
+      |M|.|.|
+      |A|.|.|
+      |S|.|.|
+    *)
+    test_calculate_num_of_matches 1 "X..M..A..S.." 3 {index= 0; character= 'X'}
+  ; "is 1 when only one match present - bottom to top"
+    >::
+    (*
+      |.|S|.|
+      |.|A|.|
+      |.|M|.|
+      |.|X|.|
+    *)
+    test_calculate_num_of_matches 1 ".S..A..M..X." 3 {index= 10; character= 'X'}
+  ; "is 1 when only one match present - left to right"
+    >::
+    (*
+      |X|M|A|S|
+    *)
+    test_calculate_num_of_matches 1 "XMAS" 4 {index= 0; character= 'X'}
+  ; "is 1 when only one match present - right to left"
+    >::
+    (*
+      |S|A|M|X|
+    *)
+    test_calculate_num_of_matches 1 "SAMX" 4 {index= 3; character= 'X'}
+  ; "is 1 when only one match present - bottom right to top left"
+    >::
+    (*
+      |S|.|.|.|
+      |.|A|.|.|
+      |.|.|M|.|
+      |.|.|.|X|
+    *)
+    test_calculate_num_of_matches 1 "S....A....M....X" 4
+      {index= 15; character= 'X'}
+  ; "is 1 when only one match present - top left to bottom right"
+    >::
+    (*
+      |X|.|.|.|
+      |.|M|.|.|
+      |.|.|A|.|
+      |.|.|.|S|
+    *)
+    test_calculate_num_of_matches 1 "X....M....A....S" 4
+      {index= 0; character= 'X'}
+  ; "is 1 when only one match present - bottom left to top right"
+    >::
+    (*
+      |.|.|.|S|
+      |.|.|A|.|
+      |.|M|.|.|
+      |X|.|.|.|
+    *)
+    test_calculate_num_of_matches 1 "...S..A..M..X..." 4
+      {index= 12; character= 'X'}
+  ; "is 1 when only one match present - top right to bottom left"
+    >::
+    (*
+      |.|.|.|X|
+      |.|.|M|.|
+      |.|A|.|.|
+      |S|.|.|.|
+    *)
+    test_calculate_num_of_matches 1 "...X..M..A..S..." 4
+      {index= 3; character= 'X'}
+  ; "is 8 when matches present in all possible directions"
+    >::
+    (*
+            |S|.|.|S|.|.|S|
+            |.|A|.|A|.|A|.|
+            |.|.|M|M|M|.|.|
+            |S|A|M|X|M|A|S|
+            |.|.|M|M|M|.|.|
+            |.|A|.|A|.|A|.|
+            |S|.|.|S|.|.|S|
+    *)
+    test_calculate_num_of_matches 8
+      "S..S..S.A.A.A...MMM..SAMXMAS..MMM...A.A.A.S..S..S" 7
+      {index= 24; character= 'X'} ]
+
+let solve_tests =
+  let test_solve have want () =
+    let actual = solve have in
+    Alcotest.(check int) "incorrect solution" want actual
+  in
+  [ ( "test solution"
+    , [ Alcotest.test_case "example is solved correctly" `Quick
+        @@ test_solve example_input 18
+      ; Alcotest.test_case "minimal example is solved correctly" `Quick
+        @@ test_solve ["..X..."; ".SAMX."; ".A..A."; "XMAS.S"; ".X...."] 4 ] )
+  ]
+
+let () =
+  let open Alcotest in
+  run "test suite for day 4 part 1" is_in_bounds_tests
+  @ calculate_num_of_matches_tests @ solve_tests