Adding the first 3 days and readme.

README.md

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+# AOC 2020
+
+Doing it in OCaml because Jay is a masochist

day1_1.ml

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+let get_one_line file =
+  try Some (input_line file) with
+    End_of_file -> None
+
+let get_lines file =
+  let rec input lines =
+    match get_one_line file with
+      Some line -> input (line :: lines)
+    | None -> List.rev lines
+  in input []
+
+let find_pair_and_prod items total =
+  let len = List.length items in
+
+  let rec check idx =
+    let left = List.nth items (idx mod len) in
+    let right = List.nth items (idx / len) in
+
+    if left + right == total
+      then left * right
+      else check (idx+1)
+  in check 0
+
+let file = "day1_1.txt"
+let channel = open_in(file)
+let lines = get_lines channel
+let ints = List.map int_of_string lines
+let prod = find_pair_and_prod ints 2020;;
+Printf.printf "%i" prod

day1_1.txt

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+1389

day1_2.hs

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+main = do
+  contents <- readFile "day1_1.txt"
+  let xs = map read $ lines contents
+  let [(i, j, k)] = [(i, j, k) | i <- [0..(length xs)-1],
+                                 j <- [0..i],
+                                 k <- [0..j],
+                                 (xs !! i) + (xs !! j) + (xs !! k) == 2020]
+  print $ (xs !! i) * (xs !! j) * (xs !! k)

day1_2.ml

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+let get_one_line file =
+  try Some (input_line file) with
+    End_of_file -> None
+
+let get_lines file =
+  let rec input lines =
+    match get_one_line file with
+      Some line -> input (line :: lines)
+    | None -> List.rev lines
+  in input []
+
+let find_pair_and_prod items total =
+  let len = List.length items in
+
+  let rec check idx =
+    let one = List.nth items (idx mod len) in
+    let two = List.nth items ((idx / len) mod len) in
+    let three = List.nth items (idx / (len * len)) in
+
+    if one + two + three == total
+      then one * two * three
+      else check (idx + 1)
+  in check 0
+
+let file = "day1_1.txt"
+let channel = open_in(file)
+let lines = get_lines channel
+let ints = List.map int_of_string lines
+let prod = find_pair_and_prod ints 202000;;
+Printf.printf "%i" prod

day2.ml

@@ -0,0 +1,50 @@
+let get_one_line file =
+  try Some (input_line file) with
+    End_of_file -> None
+
+let get_lines file =
+  let rec input lines =
+    match get_one_line file with
+      Some line -> input (line :: lines)
+    | None -> List.rev lines
+  in input []
+
+(* --- *)
+
+type password_set = { min : int; max : int; chr : char; pw : string };;
+
+let line_to_set line = (* convert a line from the file into a password_set *)
+  let [rng; chr; pw] = String.split_on_char ' ' line in (* split on spaces *)
+  let chr = String.get chr 0 in (* strip colon and convert to char *)
+  let [min; max] = List.map int_of_string (String.split_on_char '-' rng) in (* pull out the min and max from the range, map to Int *)
+  { min; max; chr; pw }
+
+(* stolen from SO.. *)
+let explode s = (* convert a string to a list of chars *)
+  let rec exp i l =
+   if i < 0 then l else exp (i - 1) (s.[i] :: l) in
+  exp (String.length s - 1) [];;
+
+let char_count el str =
+  List.length (List.filter (fun c -> c == el) (explode str))
+
+let is_valid_day1_password set =
+  let count = char_count set.chr set.pw in
+  (*Printf.printf "%s %c count: %i min: %i, max: %i, in range: %b\n" set.pw set.chr count set.min set.max (count >= set.min && count <= set.max);*)
+  count >= set.min && count <= set.max
+
+let is_valid_day2_password set =
+  let is_valid = ((String.get set.pw (set.min-1)) == set.chr) <> ((String.get set.pw (set.max-1)) == set.chr) in
+  (*Printf.printf "%s %c min: %i, max: %i, char-at-min: %c, char-at-max: %c, valid: %b\n" set.pw set.chr set.min set.max (String.get set.pw (set.min-1)) (String.get set.pw (set.max-1)) is_valid;*)
+  is_valid
+
+let file = "day2.txt"
+let channel = open_in(file)
+let lines = get_lines channel
+let sets = List.map line_to_set lines
+
+let valid_day1_passwords = List.filter is_valid_day1_password sets;;
+Printf.printf "valid day1 password count: %i\n" (List.length valid_day1_passwords)
+
+let valid_day2_passwords = List.filter is_valid_day2_password sets;;
+Printf.printf "valid day2 password count: %i\n" (List.length valid_day2_passwords)

day3.ml

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+(* Common util. Should probably put this in a module or something.. *)
+let get_one_line file =
+  try Some (input_line file) with
+    End_of_file -> None
+
+let get_lines file =
+  let rec input lines =
+    match get_one_line file with
+      Some line -> input (line :: lines)
+    | None -> List.rev lines
+  in input []
+
+let read_file file =
+  let channel = open_in(file) in
+  get_lines channel
+
+let explode s = (* convert a string to a list of chars *)
+  let rec exp i l =
+   if i < 0 then l else exp (i - 1) (s.[i] :: l) in
+  exp (String.length s - 1) [];;
+
+(* --- *)
+
+let wrapped_y y map = (* wrap the y (horizontal) coordinate when off the map *)
+  y mod (List.length (List.nth map 1))
+
+let read_cell map x y = (* return Some char at these coordinates, or None if below the map *)
+  if (x < List.length map)
+  then Some (List.nth (List.nth map x) (wrapped_y y map))
+  else None
+
+let rec go map position slope count = (* move across the map, counting trees *)
+  let (x, y) = position in
+  let (dy, dx) = slope in (* suddenly regretting having x be the vertical axis.. *)
+  match read_cell map x y with
+  | None -> count (* off the map. stop counting *)
+  | Some '#' -> go map (x+dx, y+dy) slope (count+1)
+  | Some a -> go map (x+dx, y+dy) slope count
+
+let map = read_file "day3.txt" |> List.map explode
+let slopes = [(1, 1); (3, 1); (5, 1); (7, 1); (1, 2)]
+let tree_counts = slopes |> List.map (fun slope -> go map (0, 0) slope 0);;
+
+List.iter (fun count -> Printf.printf "Number of trees: %i\n" count) tree_counts;;
+
+let product = List.fold_left ( * ) 1 tree_counts;;
+Printf.printf "Product: %i\n" product

day3.txt

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