add 2024 day 17
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2 changed files with 107 additions and 91 deletions
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.gitignore
vendored
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.gitignore
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.DS_Store
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@ -46,6 +46,32 @@ If register B contains 29, the program 1,7 would set register B to 26.
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If register B contains 2024 and register C contains 43690, the program 4,0 would set register B to 44354.
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```
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```elixir
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e1 = """
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Register A: 729
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Register B: 0
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Register C: 0
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Program: 0,1,5,4,3,0
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"""
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s1 = "4,6,3,5,6,3,5,2,1,0"
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e2 = """
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Register A: 2024
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Register B: 0
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Register C: 0
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Program: 0,3,5,4,3,0
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"""
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input = """
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Register A: 17323786
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Register B: 0
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Register C: 0
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Program: 2,4,1,1,7,5,1,5,4,1,5,5,0,3,3,0
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"""
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```
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```elixir
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defmodule ChronospatialComputer do
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defstruct a: nil, b: nil, c: nil, program: nil, pc: nil, output: <<>>
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@ -55,7 +81,12 @@ defmodule ChronospatialComputer do
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[a,b,c] = for register <- registers |> String.split("\n") do
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register |> String.split(": ") |> Enum.at(1) |> String.to_integer
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end
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pc = program |> String.split(": ") |> Enum.at(1) |> String.split(",", trim: true) |> Enum.map(&(String.to_integer/1)) |> :binary.list_to_bin()
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pc = program
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|> String.split(": ")
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|> Enum.at(1)
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|> String.split(",", trim: true)
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|> Enum.map(&(String.to_integer/1))
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|> :binary.list_to_bin()
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init(a,b,c,pc)
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end
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@ -151,106 +182,90 @@ defmodule ChronospatialComputer do
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7 -> throw "received combo op 7 at #{computer.pc + 1}"
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end
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end
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# Runs my AOC input written as Elixir with `a` in register A.
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# I could use the code that solves p1, but this runs 10x faster.
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def run_with_register_a(a), do: run_with_register_a(a, <<>>)
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def run_with_register_a(0, o), do: o
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def run_with_register_a(a, o) do
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import Bitwise
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# 0 to 7
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# 0 <= len(b) <= 3
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b = (a &&& 7)|> Bitwise.bxor(1)
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# a - 7 <= len(c) <= a
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c = a >>> b
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# 0 <= len(b) <= 3
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b = b |> Bitwise.bxor(5) |> Bitwise.bxor(c)
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o = o <> <<b &&& 7>>
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run_with_register_a(a >>> 3, o)
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end
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# finds valid values of the `A` register that will cause `run_with_register_a` to return
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# an output equal to the program
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def quine(program) do
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quine(program, 0, 10, 0)
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|> Enum.sort()
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end
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def quine(<<>>, bits, _, _), do: [bits]
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# bits is the integer so far
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# len is the number of bits to generate
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# z is the number of bits in `bits` expressed as 7 + 3*z
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def quine(<< first, rest::binary >>, bits, len, z) do
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import Bitwise
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for i <- 0..((2**len)-1), # first iter - generate 10-bit sequences, do 3-bits on all subsequent loops
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# noop on first iter - after, shifts over 7 bits
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i = i <<< (10 - len),
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# `bits` is always 7+3z bits long, so this will return 7 bits from `bits` and
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# adds the three bits from `i` at the beginning
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# so j is << i_0, i_1, i_2, b_0, b_1, b_2, b_3, b_4, b_5, b_6 >>
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j = (bits >>> 3*z) + i,
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# run the program with `j` as input
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o = ChronospatialComputer.run_with_register_a(j),
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o |> byte_size() > 0,
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# take only the sequences that generate the next output we're looking for
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# if we're on the last iteration we want sequences that don't generate
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# more outputs than we need.
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# if we're on any other iteration, we take those outputs because they
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# will be combined with more bits on the next loop.
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(rest != <<>> and o |> :binary.at(0) == first) or o == << first >> do
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# takes the `len` (either 3 or 10 - if it's the first loop) new bits from
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# `i` and prepends them to `bits`
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(i <<< 3*z) + bits
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end |> Enum.flat_map(
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fn b ->
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# generate the next three bits in the sequence
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# we do 3 at a time because the program always shifts a 3 bits after writing
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# to the output.
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quine(rest, b, 3, z+1)
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end
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)
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end
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end
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```
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```elixir
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<<12>> <> <<12>>
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Digging deeper in the device's manual, you discover the problem: this program is supposed to output another copy of the program! Unfortunately, the value in register A seems to have been corrupted. You'll need to find a new value to which you can initialize register A so that the program's output instructions produce an exact copy of the program itself.
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For example:
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```
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```elixir
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e1 = """
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Register A: 729
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Register B: 0
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Register C: 0
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Program: 0,1,5,4,3,0
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"""
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s1 = "4,6,3,5,6,3,5,2,1,0"
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e2 = """
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Register A: 2024
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Register B: 0
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Register C: 0
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Program: 0,3,5,4,3,0
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"""
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input = """
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"""
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```
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This program outputs a copy of itself if register A is instead initialized to 117440. (The original initial value of register A, 2024, is ignored.)
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What is the lowest positive initial value for register A that causes the program to output a copy of itself?
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```elixir
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[p2answer, _] = ChronospatialComputer.quine(<<2,4,1,1,7,5,1,5,4,1,5,5,0,3,3,0>>)
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```
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```elixir
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comp = input |> ChronospatialComputer.parse()
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```
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```elixir
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Stream.iterate(0, &(&1 + 1))
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|> Enum.reduce_while(
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nil,
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fn i, _ ->
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case (%ChronospatialComputer{comp | a: i}
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|> ChronospatialComputer.run_while(fn c ->
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o = c.output
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match?(^o <> _, c.program)
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end)) do
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{:halt, %ChronospatialComputer{program: p, output: p}} -> {:halt, i}
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_ -> {:cont, nil}
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end
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end
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)
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```
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```elixir
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"""
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Register A: 0
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Register B: 0
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Register C: 9
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Program: 2,6
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"""
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|> ChronospatialComputer.parse() |> ChronospatialComputer.run()
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```
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```elixir
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"""
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Register A: 10
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Register B: 0
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Register C: 0
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Program: 5,0,5,1,5,4
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"""
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|> ChronospatialComputer.parse() |> ChronospatialComputer.run()
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```
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```elixir
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"""
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Register A: 2024
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Register B: 0
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Register C: 0
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Program: 0,1,5,4,3,0
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"""
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|> ChronospatialComputer.parse() |> ChronospatialComputer.run()
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```
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```elixir
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"""
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Register A: 0
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Register B: 29
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Register C: 0
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Program: 1,7
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"""
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|> ChronospatialComputer.parse() |> ChronospatialComputer.run()
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```
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```elixir
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"""
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Register A: 0
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Register B: 2024
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Register C: 43690
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Program: 4,0
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"""
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|> ChronospatialComputer.parse() |> ChronospatialComputer.run()
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ChronospatialComputer.run_with_register_a(p2answer)
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```
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