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refactor day15 a bit

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Remove need to duplicate first value of pushable_boxes
Fail fast when left branch produces :wall in part 2
This commit is contained in:
Adam Millerchip 2024-12-17 09:59:22 +09:00
parent 0825d8db0e
commit e8a87d4a9c
1 changed files with 13 additions and 17 deletions
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30
2024/day15.exs
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@ -20,7 +20,7 @@ defmodule Day15 do
attempt_moves(next_moves, robot, warehouse) attempt_moves(next_moves, robot, warehouse)
{:ok, :box} -> {:ok, :box} ->
case get_pushable_boxes(next, move, warehouse, [next]) do case get_pushable_boxes(next, move, warehouse) do
:wall -> :wall ->
attempt_moves(next_moves, robot, warehouse) attempt_moves(next_moves, robot, warehouse)
@ -35,13 +35,14 @@ defmodule Day15 do
end end
end end
def get_pushable_boxes(box, move, warehouse, pushable_boxes) do def get_pushable_boxes(box, move, warehouse, pushable_boxes \\ []) do
next = move.(box) next = move.(box)
pushable_boxes = [box | pushable_boxes]
case Map.fetch(warehouse, next) do case Map.fetch(warehouse, next) do
:error -> pushable_boxes :error -> pushable_boxes
{:ok, :wall} -> :wall {:ok, :wall} -> :wall
{:ok, :box} -> get_pushable_boxes(next, move, warehouse, [next | pushable_boxes]) {:ok, :box} -> get_pushable_boxes(next, move, warehouse, pushable_boxes)
end end
end end
@ -78,7 +79,7 @@ defmodule Day15 do
attempt_moves2(next_moves, robot, warehouse) attempt_moves2(next_moves, robot, warehouse)
{:ok, {:box, side}} -> {:ok, {:box, side}} ->
case get_pushable_boxes2(next, side, move, warehouse, [{next, side}]) do case get_pushable_boxes2(next, side, move, warehouse) do
:wall -> :wall ->
attempt_moves2(next_moves, robot, warehouse) attempt_moves2(next_moves, robot, warehouse)
@ -102,8 +103,9 @@ defmodule Day15 do
# [][] []<--make sure RHS moves too # [][] []<--make sure RHS moves too
# [] # []
# @<- pushing up pushes all # @<- pushing up pushes all
def get_pushable_boxes2(box, side, move, warehouse, pushable_boxes) do def get_pushable_boxes2(box, side, move, warehouse, pushable_boxes \\ []) do
next = move.(box) next = move.(box)
pushable_boxes = [{box, side} | pushable_boxes]
case abs(elem(next, 1) - elem(box, 1)) do case abs(elem(next, 1) - elem(box, 1)) do
# horizontal # horizontal
@ -116,9 +118,7 @@ defmodule Day15 do
:wall :wall
{:ok, {:box, next_side}} -> {:ok, {:box, next_side}} ->
get_pushable_boxes2(next, next_side, move, warehouse, [ get_pushable_boxes2(next, next_side, move, warehouse, pushable_boxes)
{next, next_side} | pushable_boxes
])
end end
# vertical # vertical
@ -154,27 +154,23 @@ defmodule Day15 do
:wall :wall
{{{:ok, {:box, side}}, :error}, left, _right} -> {{{:ok, {:box, side}}, :error}, left, _right} ->
get_pushable_boxes2(left, side, move, warehouse, [{left, side} | pushable_boxes]) get_pushable_boxes2(left, side, move, warehouse, pushable_boxes)
{{:error, {:ok, {:box, side}}}, _left, right} -> {{:error, {:ok, {:box, side}}}, _left, right} ->
get_pushable_boxes2(right, side, move, warehouse, [{right, side} | pushable_boxes]) get_pushable_boxes2(right, side, move, warehouse, pushable_boxes)
{{{:ok, {:box, :left}}, {:ok, {:box, :right}}}, left, _} -> {{{:ok, {:box, :left}}, {:ok, {:box, :right}}}, left, _} ->
# if left-right, just one box, only need to check one side # if left-right, just one box, only need to check one side
# [] # []
# [] # []
get_pushable_boxes2(left, :left, move, warehouse, [{left, :left} | pushable_boxes]) get_pushable_boxes2(left, :left, move, warehouse, pushable_boxes)
{{{:ok, {:box, :right}}, {:ok, {:box, :left}}}, left, right} -> {{{:ok, {:box, :right}}, {:ok, {:box, :left}}}, left, right} ->
# if right-left, two boxes, so need to check both... # if right-left, two boxes, so need to check both...
# [][] # [][]
# [] # []
left = get_pushable_boxes2(left, :right, move, warehouse, [{left, :right}]) with left when left != :wall <- get_pushable_boxes2(left, :right, move, warehouse, []),
right = get_pushable_boxes2(right, :left, move, warehouse, [{right, :left}]) right when right != :wall <- get_pushable_boxes2(right, :left, move, warehouse, []) do
if left == :wall or right == :wall do
:wall
else
pushable_boxes ++ left ++ right pushable_boxes ++ left ++ right
end end
end end