You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
36 lines
1.1 KiB
Elixir
36 lines
1.1 KiB
Elixir
1 month ago
|
defmodule Day7 do
|
||
|
|
def run do
|
||
|
|
lines =
|
||
|
|
File.read!("test.txt")
|
||
|
|
|> String.split("\n")
|
||
|
|
|> Enum.map(fn l -> String.split(l, ~r{\D+}) |> Enum.map(&String.to_integer(&1)) end)
|
||
|
|
|> Enum.map(fn [head | tail] -> {head, tail} end)
|
||
|
|
|
||
|
|
[part1, part2] =
|
||
|
|
Enum.map([1, 2], fn part ->
|
||
|
|
# filter valid lines for parts 1 and 2, grab their targets, and sum them
|
||
|
|
Enum.filter(lines, &valid?(&1, part)) |> Enum.map(&elem(&1, 0)) |> Enum.sum()
|
||
|
|
end)
|
||
|
|
|
||
|
|
dbg({part1, part2})
|
||
|
|
end
|
||
|
|
|
||
|
|
defp valid?({total, [a, b | rest]}, part) do
|
||
|
|
# if we're in part 1, just check a * b and a + b. in part 2, we'll also check a <> b
|
||
|
|
branches = if part == 1, do: [a * b, a + b], else: [a * b, a + b, concat(a, b)]
|
||
|
|
|
||
|
|
case [a, b | rest] do
|
||
|
|
# base case is 2 elements. if any succeed, return true
|
||
|
|
[_, _] -> Enum.any?(branches, fn n -> n == total end)
|
||
|
|
# recurse by trying each branch, subbing the first 2 elements with the new combined element
|
||
|
|
[_, _ | rest] -> Enum.any?(branches, &valid?({total, [&1 | rest]}, 2))
|
||
|
|
end
|
||
|
|
end
|
||
|
|
|
||
|
|
defp concat(a, b) do
|
||
|
|
"#{a}#{b}" |> String.to_integer()
|
||
|
|
end
|
||
|
|
end
|
||
|
|
|
||
|
|
Day7.run()
|