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|
defmodule Day06 do
def parse_data(data) do
grid = data
|> String.split("\n", trim: true)
guard = grid
|> map_elements("^")
|> hd()
obstacles = grid
|> map_elements("#")
obstacles_vert = obstacles
|> Enum.group_by(fn {i, _} -> i end, fn {_, j} -> j end)
|> Enum.map(fn {k, v} -> {k, v |> :gb_sets.from_list()} end)
|> Map.new()
obstacles_hori = obstacles
|> Enum.group_by(fn {_, j} -> j end, fn {i, _} -> i end)
|> Enum.map(fn {k, v} -> {k, v |> :gb_sets.from_list()} end)
|> Map.new()
grid = grid
|> Enum.map(& :array.from_list(String.codepoints(&1)))
|> :array.from_list()
{guard, grid, obstacles_vert, obstacles_hori}
end
def map_elements(grid, element) do
for {line, i} <- Enum.with_index(grid),
{v, j} <- Enum.with_index(String.codepoints(line)) do
if v == element do
{i, j}
end
end
|> Enum.filter(& &1 != nil)
end
def part1({guard, grid, _, _}) do
path(guard, :up, grid)
|> Enum.map(fn {i, j, _} -> {i, j} end)
|> Enum.uniq()
|> Enum.count()
end
def path(acc \\ [], {i, j}, dir, grid) do
acc = [{i, j, dir} | acc]
{ni, nj, ndir} = next(i, j, dir)
case check(ni, nj, grid) do
:invalid ->
acc
:obstacle ->
path(tl(acc), {i, j}, ndir, grid)
:valid ->
path(acc, {ni, nj}, dir, grid)
end
end
def next(i, j, dir) do
case dir do
:up ->
{i-1, j, :right}
:right ->
{i, j+1, :down}
:down ->
{i+1, j, :left}
:left ->
{i, j-1, :up}
end
end
def check(i, j, grid, extra \\ nil) do
cond do
i < 0
or i == :array.size(grid)
or j < 0
or j == :array.get(i, grid) |> :array.size() ->
:invalid
:array.get(j, :array.get(i, grid)) == "#"
or {i, j} == extra ->
:obstacle
true ->
:valid
end
end
def part2({guard, grid, overt, ohori}) do
path(guard, :up, grid)
|> Enum.map(fn {i, j, _} -> {i, j} end)
|> Enum.uniq()
|> Enum.filter(& &1 != guard)
|> Enum.map(fn {i, j} ->
is_loop?(guard, :up, grid, update(overt, i, j), update(ohori, j, i))
end)
|> Enum.count(& &1)
end
def update(m, k, v) do
Map.get_and_update(m, k, fn set ->
case set do
nil ->
{set, :gb_sets.from_list([v])}
set ->
{set, :gb_sets.add(v, set)}
end
end)
|> elem(1)
end
def next(i, j, dir, overt, ohori) do
case dir do
:up ->
case :gb_sets.smaller(i, Map.get(ohori, j, :gb_sets.empty())) do
:none ->
:out
{_, v} ->
{v+1, j, :right}
end
:right ->
case :gb_sets.larger(j, Map.get(overt, i, :gb_sets.empty())) do
:none ->
:out
{_, v} ->
{i, v-1, :down}
end
:down ->
case :gb_sets.larger(i, Map.get(ohori, j, :gb_sets.empty())) do
:none ->
:out
{_, v} ->
{v-1, j, :left}
end
:left ->
case :gb_sets.smaller(j, Map.get(overt, i, :gb_sets.empty())) do
:none ->
:out
{_, v} ->
{i, v+1, :up}
end
end
end
def is_loop?(cache \\ MapSet.new(), {i, j}, dir, grid, overt, ohori) do
key = {i, j, dir}
if MapSet.member?(cache, key) do
true
else
case next(i, j, dir, overt, ohori) do
:out ->
false
{ni, nj, ndir} ->
is_loop?(MapSet.put(cache, key), {ni, nj}, ndir, grid, overt, ohori)
end
end
end
end
data = IO.read(:stdio, :eof) |> Day06.parse_data()
{time1 , ans1} = :timer.tc(fn -> Day06.part1(data) end)
IO.puts("Time : #{time1 / 1000000}")
IO.puts("Answer: #{ans1}")
{time2 , ans2} = :timer.tc(fn -> Day06.part2(data) end)
IO.puts("Time : #{time2 / 1000000}")
IO.puts("Answer: #{ans2}")
|
