From 6541e2362af54e0dca844a1dff0f964a566bd05b Mon Sep 17 00:00:00 2001
From: Dustin Swan <dustin@dustinswan.com>
Date: Fri, 11 Dec 2020 13:37:20 -0500
Subject: [PATCH] day 10

---
 day10.ml  |  73 ++++++++++++++++++++++++++++++++++++
 day10.txt | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 183 insertions(+)
 create mode 100644 day10.ml
 create mode 100644 day10.txt

diff --git a/day10.ml b/day10.ml
new file mode 100644
index 0000000..879943f
--- /dev/null
+++ b/day10.ml
@@ -0,0 +1,73 @@
+(* 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 (>>) f g x = g(f(x))
+
+let list_max l = List.fold_left (fun acc x -> if x > acc then x else acc) (List.hd l) l
+
+let map_tuple f (a, b) = (f a, f b)
+
+let memo_rec f =
+  let h = Hashtbl.create 1000 in
+  let rec g x =
+    try Hashtbl.find h x
+    with Not_found ->
+      let y = f g x in
+      Hashtbl.add h x y;
+      y
+  in g
+
+(* --- *)
+
+let rec collect_diffs = function
+  | x :: y :: [] -> [y - x] (* 2 elemnts left *)
+  | x :: y :: z -> y - x :: collect_diffs (y :: z)
+
+let count_steps = (* returns a tuple of counts of 1's and 3's *)
+  List.partition (Int.equal 1)
+  >> map_tuple List.length
+
+let count_valid self = function
+  | x :: y :: [] -> if y - x < 4 then 1 else 0
+  | x :: y :: rest ->
+      if y - x > 3
+      then 0
+      else self (x :: rest) + self (y :: rest)
+
+let count_valid_memo = memo_rec count_valid
+
+let () =
+  let lines = read_file "day10.txt"
+    |> List.map int_of_string
+  in
+
+  let adapter_jolts = 3 + list_max lines in
+
+  let sorted = lines
+    |> List.cons adapter_jolts (* add our adapter *)
+    |> List.cons 0 (* add the outlet *)
+    |> List.sort (fun x y -> if x > y then 1 else if x < y then -1 else 0)
+  in
+
+  sorted
+    |> collect_diffs
+    |> count_steps
+    |> fun (x, y) -> x * y
+    |> Printf.printf "prod: %i\n";
+
+  sorted
+    |> count_valid_memo
+    |> Printf.printf "\nsum: %i\n"
diff --git a/day10.txt b/day10.txt
new file mode 100644
index 0000000..46ad475
--- /dev/null
+++ b/day10.txt
@@ -0,0 +1,110 @@
+160
+34
+123
+159
+148
+93
+165
+56
+179
+103
+171
+44
+110
+170
+147
+98
+25
+37
+137
+71
+5
+6
+121
+28
+19
+134
+18
+7
+66
+90
+88
+181
+89
+41
+156
+46
+8
+61
+124
+9
+161
+72
+13
+172
+111
+59
+105
+51
+109
+27
+152
+117
+52
+68
+95
+164
+116
+75
+78
+180
+81
+47
+104
+12
+133
+175
+16
+149
+135
+99
+112
+38
+67
+53
+153
+2
+136
+113
+17
+145
+106
+31
+45
+169
+146
+168
+26
+36
+118
+62
+65
+142
+130
+1
+140
+84
+94
+141
+122
+22
+48
+102
+60
+178
+127
+73
+74
+87
+182
+35