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author | Alexandre Jesus <adbjesus@gmail.com> | 2024-12-21 13:53:30 +0000 |
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committer | Alexandre Jesus <adbjesus@gmail.com> | 2024-12-21 13:53:30 +0000 |
commit | 1919d9a5cc1c4ca03c0a72098113e2bc366116cc (patch) | |
tree | 40b32cdf2692e7d8ce5ddff4ff3d6a03b0fb4434 /src/day17.exs | |
parent | 11ab619de9e4d4116dd7727347a9eba9dd72c584 (diff) | |
download | aoc2024-1919d9a5cc1c4ca03c0a72098113e2bc366116cc.tar.gz aoc2024-1919d9a5cc1c4ca03c0a72098113e2bc366116cc.zip |
Day 17
Diffstat (limited to 'src/day17.exs')
-rw-r--r-- | src/day17.exs | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/src/day17.exs b/src/day17.exs new file mode 100644 index 0000000..9f9db29 --- /dev/null +++ b/src/day17.exs @@ -0,0 +1,127 @@ +defmodule Day17 do + defmodule Computer do + @derive Inspect + @enforce_keys [:a, :b, :c, :out, :instructions, :pointer] + defstruct @enforce_keys + + def from_data(data) do + [a, b, c | instructions] = Regex.scan(~r/\d+/, data) + |> Enum.map(&String.to_integer(hd(&1))) + + %Computer{a: a, b: b, c: c, out: [], instructions: instructions, pointer: 0} + end + + def run(comp) do + case instruction(comp) do + {:halt, comp} -> + comp + {:ok, comp} -> + run(comp) + end + end + + defp instruction(comp) do + case comp.instructions |> Enum.drop(comp.pointer) do + [] -> + {:halt, comp} + [0, r | _] -> + cr = combo(comp, r) + {:ok, %Computer{comp | a: Bitwise.bsr(comp.a, cr), pointer: comp.pointer+2}} + [1, r | _] -> + {:ok, %Computer{comp | b: Bitwise.bxor(comp.b, r), pointer: comp.pointer+2}} + [2, r | _] -> + cr = combo(comp, r) + {:ok, %Computer{comp | b: rem(cr, 8), pointer: comp.pointer+2}} + [3, r | _] -> + if comp.a == 0 do + {:ok, %Computer{comp | pointer: comp.pointer+2}} + else + {:ok, %Computer{comp | pointer: r}} + end + [4, _ | _] -> + {:ok, %Computer{comp | b: Bitwise.bxor(comp.b, comp.c), pointer: comp.pointer+2}} + [5, r | _] -> + cr = combo(comp, r) + {:ok, %Computer{comp | out: [rem(cr, 8) | comp.out], pointer: comp.pointer+2}} + [6, r | _] -> + cr = combo(comp, r) + {:ok, %Computer{comp | b: Bitwise.bsr(comp.a, cr), pointer: comp.pointer+2}} + [7, r | _] -> + cr = combo(comp, r) + {:ok, %Computer{comp | c: Bitwise.bsr(comp.a, cr), pointer: comp.pointer+2}} + end + end + + defp combo(comp, v) do + case v do + 0 -> 0 + 1 -> 1 + 2 -> 2 + 3 -> 3 + 4 -> comp.a + 5 -> comp.b + 6 -> comp.c + 7 -> raise "Invalid combo operand (7)" + end + end + end + + def part1(data) do + data + |> Computer.from_data() + |> Computer.run() + |> then(& &1.out) + |> Enum.reverse() + |> Enum.join(",") + end + + def part2(data) do + data + |> Computer.from_data() + |> then(& &1.instructions) + |> Enum.reverse() + |> solve2(0) + end + + defp solve2(rout, a) do + case rout do + [] -> + a + [h | t] -> + # I deduced the following by hand for my input, but maybe it could + # have been done programatically. An important takeway is that + # (for my input, and probably for all) `a` incerases by 3 bits for each + # iteration of the program. AS such, we can only need to check the + # possibilities over the last 3 bits (a..a+7) in each iteration ourselves + a = Bitwise.bsl(a, 3) + possible = a..a+7 + |> Enum.filter(fn a -> + Bitwise.band(a, 7) + |> Bitwise.bxor(5) + |> Bitwise.bxor(6) + |> Bitwise.bxor(Bitwise.bsr(a, Bitwise.band(a, 7) |> Bitwise.bxor(5))) + |> Bitwise.band(7) == h + end) + + case possible do + [] -> + :none + possible -> + possible + |> Enum.map(& solve2(t, &1)) + |> Enum.find(& &1 != :none) + || :none + end + end + end +end + +data = IO.read(:stdio, :eof) + +{time1, ans1} = :timer.tc(fn -> Day17.part1(data) end) +IO.puts("Time : #{time1 / 1000000}") +IO.puts("Answer: #{ans1}") + +{time2, ans2} = :timer.tc(fn -> Day17.part2(data) end) +IO.puts("Time : #{time2 / 1000000}") +IO.puts("Answer: #{ans2}") |