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-rw-r--r--src/day07.exs70
1 files changed, 34 insertions, 36 deletions
diff --git a/src/day07.exs b/src/day07.exs
index 1adeb54..0ec37b6 100644
--- a/src/day07.exs
+++ b/src/day07.exs
@@ -6,52 +6,50 @@ defmodule Utils do
end
end
-defmodule Equation do
- @derive Inspect
- defstruct [:result, :terms]
-
- def from_string(string) do
- string
- |> Utils.parse_integer_list([":", " "])
- |> then(& %Equation{result: hd(&1), terms: tl(&1)})
- end
+defmodule Day07 do
+ defmodule Equation do
+ @derive Inspect
+ defstruct [:result, :terms]
- def has_lr_solution(equation, ops) do
- has_lr_solution(hd(equation.terms), tl(equation.terms), equation.result, ops)
- end
+ def from_string(string) do
+ string
+ |> Utils.parse_integer_list([":", " "])
+ |> then(& %Equation{result: hd(&1), terms: tl(&1)})
+ end
- defp has_lr_solution(acc, terms, result, ops) do
- cond do
- acc > result ->
- false
- terms == [] and acc == result ->
- true
- terms == [] ->
- false
- true ->
- ops
- |> Enum.any?(& has_lr_solution(apply_op(acc, hd(terms), &1), tl(terms), result, ops))
+ def lr_solution?(equation, ops) do
+ lr_solution_rev?(equation.result, Enum.reverse(equation.terms), ops)
end
- end
- defp apply_op(l, r, op) do
- case op do
- :add ->
- l + r
- :mul ->
- l * r
- :concat ->
- String.to_integer("#{l}#{r}")
+ defp lr_solution_rev?(result, terms, ops) do
+ cond do
+ terms == [] and result == 0 ->
+ true
+ terms == [] or result == 0 ->
+ false
+ true ->
+ ops
+ |> Enum.map(& apply_op_rev(result, hd(terms), &1))
+ |> Enum.filter(&Kernel.is_integer/1)
+ |> Enum.any?(& lr_solution_rev?(&1, tl(terms), ops))
+ end
end
+
+ defp apply_op_rev(l, r, :add), do: l >= r and l-r
+ defp apply_op_rev(l, r, :mul), do: rem(l, r) == 0 and div(l, r)
+ defp apply_op_rev(l, r, :concat), do: uncat(l, r)
+
+ defp uncat(l, 0), do: l
+ defp uncat(0, _), do: false
+ defp uncat(l, r) when rem(l, 10) == rem(r, 10), do: uncat(div(l, 10), div(r, 10))
+ defp uncat(_, _), do: false
end
-end
-defmodule Day07 do
def part1(data) do
data
|> String.split("\n", trim: true)
|> Enum.map(& Equation.from_string(&1))
- |> Enum.filter(& Equation.has_lr_solution(&1, [:mul, :add]))
+ |> Enum.filter(& Equation.lr_solution?(&1, [:mul, :add]))
|> Enum.map(& &1.result)
|> Enum.sum()
end
@@ -60,7 +58,7 @@ defmodule Day07 do
data
|> String.split("\n", trim: true)
|> Enum.map(& Equation.from_string(&1))
- |> Enum.filter(& Equation.has_lr_solution(&1, [:mul, :concat, :add]))
+ |> Enum.filter(& Equation.lr_solution?(&1, [:mul, :concat, :add]))
|> Enum.map(& &1.result)
|> Enum.sum()
end