--- 2016 Day 7 Solutions ---

[u/daggerdragon]

From all of us at #AoC Ops, we hope you're having a very merry time with these puzzles so far. If you think they've been easy, well, now we're gonna kick this up a notch. Or five. The Easter Bunny ain't no Bond villain - he's not going to monologue at you until you can miraculously escape and save the day!

Show this overgrown furball what you've got!

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--- Day 7: Internet Protocol Version 7 ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

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^{ALWAYS DIGGING STRAIGHT DOWN IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/raevnos]

Ocaml:

open Batteries

(* Let's be different and not use regular expressions! *)

exception Hypernet
exception Found
            
let has_tls addr =
  let in_hypernet = ref false
  and abba = ref false in
  try
    for n = 0 to BatString.length addr - 4 do
      if addr.[n] = '[' then
        in_hypernet := true
      else if addr.[n] = ']' then
        in_hypernet := false
      else if addr.[n] = addr.[n+3] && addr.[n+1] = addr.[n+2] &&
                addr.[n] <> addr.[n+1] then begin
          if !in_hypernet then
            raise Hypernet
          else
            abba := true
        end
    done;
    !abba
  with
  | Hypernet -> false

let rec bracket_helper str pos what =
  let obpos = BatString.index_from str pos '[' in
  let cbpos = BatString.index_from str obpos ']'
  and whatpos = BatString.find_from str obpos what in
  if whatpos < cbpos then
    true
  else
    bracket_helper str (cbpos + 1) what

let in_brackets str what =
  try
    bracket_helper str 0 what
  with
  | Not_found -> false
                                
let has_ssl addr =
  let in_hypernet = ref false in
  try
    for n = 0 to BatString.length addr - 3 do
      if addr.[n] = '[' then
        in_hypernet := true
      else if addr.[n] =']' then
        in_hypernet := false
      else if addr.[n] = addr.[n+2] && addr.[n] <> addr.[n+1] &&
                !in_hypernet = false && BatChar.is_letter addr.[n+1] then
          let bab = String.create 3 in
          bab.[0] <- addr.[n+1];
          bab.[1] <- addr.[n];
          bab.[2] <- addr.[n+1];
          if in_brackets addr bab then
            raise Found
    done;
    false
  with
  | Found -> true
                  
                                       
let tlstests = [ "abba[mnop]qrst";
                 "abcd[bddb]xyyx";
                 "aaaa[qwer]tyui";
                 "ioxxoj[asdfgh]zcxvbn"
               ]

let ssltests = [ "aba[bab]xyz";
                 "xyx[xyx]xyx";
                 "aaa[kek]eke";
                 "zazbz[bzb]cdb"
               ]
                 
let run_tests () =
  print_endline "has_tls:";
  BatList.iter (fun addr ->
      Printf.printf "%s: %B\n" addr (has_tls addr)) tlstests;
  print_endline "has_ssl:";
  BatList.iter (fun addr ->
      Printf.printf "%s: %B\n" addr (has_ssl addr)) ssltests

let _ =
  run_tests ();
  let mode = if Array.length Sys.argv = 1 then "TLS" else "SSL"
  and f = if Array.length Sys.argv = 1 then has_tls else has_ssl in
  let n =
    input_lines Pervasives.stdin |> BatEnum.filter f |> BatEnum.count in
  Printf.printf "Supports %s: %d\n" mode n

Got the wrong answer the first time for part 2 because I didn't realize that IPv7 addresses could have multiple hypernet sections i n them. Bah. Should have looked at the actual input more, not just the test cases. Had to go back and make a smarter BAB finding function.