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|
defmodule Day16 do
defmodule State do
@enforce_keys [:pqueue, :map, :path, :dist]
defstruct [:pqueue, :map, :path, :dist]
def new(game) do
pqueue = :gb_sets.from_list([{0, game.start}])
map = :gb_trees.insert(game.start, 0, :gb_trees.empty())
path = Map.new([{game.start, []}])
dist = Map.new([{game.start, 0}])
%State{pqueue: pqueue, map: map, path: path, dist: dist}
end
def upsert(state, posdir, dist, prev) do
case :gb_trees.lookup(posdir, state.map) do
:none ->
pqueue = :gb_sets.insert({dist, posdir}, state.pqueue)
map = :gb_trees.insert(posdir, dist, state.map)
path = Map.put(state.path, posdir, [prev])
distmap = Map.update(state.dist, posdir, dist, &min(&1, dist))
%State{pqueue: pqueue, map: map, path: path, dist: distmap}
{_, odist} ->
distmap = Map.update!(state.dist, posdir, &min(&1, dist))
cond do
dist > odist ->
%State{state | dist: distmap}
dist == odist ->
path = Map.update!(state.path, posdir, &[prev | &1])
%State{state | path: path, dist: distmap}
true ->
pqueue = :gb_sets.delete({odist, posdir}, state.pqueue)
pqueue = :gb_sets.insert({dist, posdir}, pqueue)
map = :gb_trees.update(posdir, dist, state.map)
path = Map.put(state.path, posdir, [prev])
%State{pqueue: pqueue, map: map, path: path, dist: distmap}
end
end
end
def empty?(state) do
:gb_sets.is_empty(state.pqueue)
end
def pop(state) do
{v, pqueue} = :gb_sets.take_smallest(state.pqueue)
{v, %State{state | pqueue: pqueue}}
end
def optimal_dist(state, node) do
state.dist
|> Enum.filter(fn {{pos, _}, _} -> pos == node end)
|> Enum.map(fn {_, v} -> v end)
|> Enum.min()
end
def optimal_path_nodes(state, node) do
nodes = state.dist
|> Enum.filter(fn {{pos, _}, _} -> pos == node end)
mindist = nodes
|> Enum.map(fn {_, v} -> v end)
|> Enum.min()
nodes = nodes
|> Enum.filter(fn {_, v} -> v == mindist end)
|> Enum.map(fn {posdir, _} -> posdir end)
optimal_path_nodes(state, nodes, [])
end
defp optimal_path_nodes(state, queue, acc) do
case queue do
[] ->
acc
|> Enum.map(fn {pos, _} -> pos end)
|> Enum.uniq()
[h | t] ->
acc = [h | acc]
queue = Map.fetch!(state.path, h) ++ t
optimal_path_nodes(state, queue, acc)
end
end
end
defmodule Game do
@derive Inspect
defstruct [:grid, :start, :end]
def from_data(data) do
grid = data
|> String.split("\n", trim: true)
|> Enum.with_index()
|> Enum.flat_map(fn {s, i} ->
String.codepoints(s)
|> Enum.with_index()
|> Enum.map(fn {c, j} -> {{i, j}, c} end)
end)
|> Map.new()
start = grid
|> Enum.find_value(fn {pos, c} -> c == "S" and pos end)
|> then(& {&1, :right})
endpos = grid
|> Enum.find_value(fn {pos, c} -> c == "E" and pos end)
%Game{grid: grid, start: start, end: endpos}
end
def shortest(game) do
game
|> shortest(State.new(game))
|> State.optimal_dist(game.end)
end
def shortest_path_nodes(game) do
game
|> shortest(State.new(game))
|> State.optimal_path_nodes(game.end)
end
defp shortest(game, state) do
if State.empty?(state) do
state
else
{{dist, {pos, dir}}, state} = State.pop(state)
if pos == game.end do
shortest(game, state)
else
neighbors(game, {dist, {pos, dir}})
for {ndist, nposdir} <- neighbors(game, {dist, {pos, dir}}), reduce: state do
state -> State.upsert(state, nposdir, ndist, {pos, dir})
end
|> then(& shortest(game, &1))
end
end
end
defp neighbors(game, {dist, {{i, j}, dir}}) do
case dir do
:right ->
[{dist+1, {{i, j+1}, :right}},
{dist+1001, {{i-1, j}, :up}},
{dist+1001, {{i+1, j}, :down}},
{dist+2001, {{i, j-1}, :left}}]
:left ->
[{dist+1, {{i, j-1}, :left}},
{dist+1001, {{i-1, j}, :up}},
{dist+1001, {{i+1, j}, :down}},
{dist+2001, {{i, j+1}, :right}}]
:up ->
[{dist+1, {{i-1, j}, :up}},
{dist+1001, {{i, j-1}, :left}},
{dist+1001, {{i, j+1}, :right}},
{dist+2001, {{i+1, j}, :down}}]
:down ->
[{dist+1, {{i+1, j}, :down}},
{dist+1001, {{i, j-1}, :left}},
{dist+1001, {{i, j+1}, :right}},
{dist+2001, {{i-1, j}, :up}}]
end
|> Enum.filter(fn {_, {p, _}} ->
case Map.fetch(game.grid, p) do
:error -> false
{:ok, "#"} -> false
_ -> true
end
end)
end
end
def part1(data) do
data
|> Game.from_data()
|> Game.shortest()
end
def part2(data) do
data
|> Game.from_data()
|> Game.shortest_path_nodes()
|> Enum.count()
end
end
data = IO.read(:stdio, :eof)
{time1, ans1} = :timer.tc(fn -> Day16.part1(data) end)
IO.puts("Time : #{time1 / 1000000}")
IO.puts("Answer: #{ans1}")
{time2, ans2} = :timer.tc(fn -> Day16.part2(data) end)
IO.puts("Time : #{time2 / 1000000}")
IO.puts("Answer: #{ans2}")
|
