2024-12-15 10:15:52 +00:00
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#!/usr/bin/env elixir
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defmodule Day15 do
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def part1({warehouse, robot, moves}) do
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attempt_moves(moves, robot, warehouse)
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2024-12-15 17:55:05 +00:00
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|> Enum.filter(&match?({_, :box}, &1))
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|> Enum.map(fn {{x, y}, :box} -> x + y * 100 end)
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|> Enum.sum()
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end
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def attempt_moves([], _robot, warehouse), do: warehouse
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def attempt_moves([move | next_moves], robot, warehouse) do
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next = move.(robot)
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case Map.fetch(warehouse, next) do
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:error ->
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attempt_moves(next_moves, next, warehouse)
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{:ok, :wall} ->
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attempt_moves(next_moves, robot, warehouse)
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{:ok, :box} ->
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case get_pushable_boxes(next, move, warehouse) do
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2024-12-15 10:15:52 +00:00
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:wall ->
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attempt_moves(next_moves, robot, warehouse)
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boxes ->
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warehouse =
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Enum.reduce(boxes, warehouse, fn box, warehouse ->
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warehouse |> Map.delete(box) |> Map.put(move.(box), :box)
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end)
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attempt_moves(next_moves, next, warehouse)
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end
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end
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end
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2024-12-17 00:59:22 +00:00
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def get_pushable_boxes(box, move, warehouse, pushable_boxes \\ []) do
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2024-12-15 10:15:52 +00:00
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next = move.(box)
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pushable_boxes = [box | pushable_boxes]
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2024-12-15 10:15:52 +00:00
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case Map.fetch(warehouse, next) do
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:error -> pushable_boxes
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{:ok, :wall} -> :wall
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2024-12-17 00:59:22 +00:00
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{:ok, :box} -> get_pushable_boxes(next, move, warehouse, pushable_boxes)
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2024-12-15 10:15:52 +00:00
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end
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end
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2024-12-15 17:55:05 +00:00
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def part2({warehouse, {x, y}, moves}) do
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bigger_warehouse =
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Enum.reduce(warehouse, %{}, fn {{x, y}, v}, bigger ->
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{left, right} =
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case v do
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:box -> {{:box, :left}, {:box, :right}}
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:wall -> {:wall, :wall}
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end
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bigger |> Map.put({x * 2, y}, left) |> Map.put({x * 2 + 1, y}, right)
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end)
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robot = {x * 2, y}
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attempt_moves2(moves, robot, bigger_warehouse)
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|> Enum.filter(&match?({_, {:box, :left}}, &1))
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|> Enum.map(fn {{x, y}, {:box, :left}} -> x + y * 100 end)
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|> Enum.sum()
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end
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def attempt_moves2([], _robot, warehouse), do: warehouse
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def attempt_moves2([move | next_moves], robot, warehouse) do
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next = move.(robot)
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case Map.fetch(warehouse, next) do
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:error ->
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attempt_moves2(next_moves, next, warehouse)
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{:ok, :wall} ->
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attempt_moves2(next_moves, robot, warehouse)
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{:ok, {:box, side}} ->
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case get_pushable_boxes2(next, side, move, warehouse) do
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:wall ->
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attempt_moves2(next_moves, robot, warehouse)
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boxes ->
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new_boxes = Map.new(boxes, fn {box, side} -> {move.(box), {:box, side}} end)
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warehouse =
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warehouse
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|> Map.drop(Enum.map(boxes, &elem(&1, 0)))
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|> Map.merge(new_boxes)
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attempt_moves2(next_moves, next, warehouse)
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end
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end
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end
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# need to account for 2-width boxes when pushing vertically
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# @<--pushing down moves down all RHS of stack
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# [][][][]
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# [][][] @
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# [][] []<--make sure RHS moves too
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# []
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# @<- pushing up pushes all
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def get_pushable_boxes2(box, side, move, warehouse, pushable_boxes \\ []) do
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next = move.(box)
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pushable_boxes = [{box, side} | pushable_boxes]
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case abs(elem(next, 1) - elem(box, 1)) do
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# horizontal
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0 ->
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case Map.fetch(warehouse, next) do
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:error ->
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pushable_boxes
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{:ok, :wall} ->
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:wall
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{:ok, {:box, next_side}} ->
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get_pushable_boxes2(next, next_side, move, warehouse, pushable_boxes)
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end
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# vertical
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1 ->
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{x, y} = box
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{other_box, other_side} =
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case side do
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:left -> {{x + 1, y}, :right}
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:right -> {{x - 1, y}, :left}
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end
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other_next = move.(other_box)
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pushable_boxes = [{other_box, other_side} | pushable_boxes]
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side
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|> case do
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:left ->
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{{Map.fetch(warehouse, next), Map.fetch(warehouse, other_next)}, next, other_next}
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:right ->
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{{Map.fetch(warehouse, other_next), Map.fetch(warehouse, next)}, other_next, next}
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end
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|> case do
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{{:error, :error}, _, _} ->
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pushable_boxes
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{{{:ok, :wall}, _}, _, _} ->
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:wall
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{{_, {:ok, :wall}}, _, _} ->
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:wall
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{{{:ok, {:box, side}}, :error}, left, _right} ->
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2024-12-17 00:59:22 +00:00
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get_pushable_boxes2(left, side, move, warehouse, pushable_boxes)
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2024-12-15 17:55:05 +00:00
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{{:error, {:ok, {:box, side}}}, _left, right} ->
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2024-12-17 00:59:22 +00:00
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get_pushable_boxes2(right, side, move, warehouse, pushable_boxes)
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{{{:ok, {:box, :left}}, {:ok, {:box, :right}}}, left, _} ->
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# if left-right, just one box, only need to check one side
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# []
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# []
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get_pushable_boxes2(left, :left, move, warehouse, pushable_boxes)
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{{{:ok, {:box, :right}}, {:ok, {:box, :left}}}, left, right} ->
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# if right-left, two boxes, so need to check both...
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# [][]
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# []
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2024-12-17 00:59:22 +00:00
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with left when left != :wall <- get_pushable_boxes2(left, :right, move, warehouse, []),
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right when right != :wall <- get_pushable_boxes2(right, :left, move, warehouse, []) do
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pushable_boxes ++ left ++ right
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end
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end
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end
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2024-12-15 10:15:52 +00:00
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end
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def input do
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with [input_filename] <- System.argv(),
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{:ok, input} <- File.read(input_filename) do
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[raw_map, raw_moves] = String.split(input, "\n\n")
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{_, _y, robot, map} =
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for <<char::binary-1 <- raw_map <> "\n">>, reduce: {0, 0, nil, %{}} do
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{x, y, robot, map} ->
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case char do
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"." -> {x + 1, y, robot, map}
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"#" -> {x + 1, y, robot, Map.put(map, {x, y}, :wall)}
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"O" -> {x + 1, y, robot, Map.put(map, {x, y}, :box)}
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"@" -> {x + 1, y, {x, y}, map}
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"\n" -> {0, y + 1, robot, map}
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end
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end
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moves =
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for <<char::binary-1 <- String.replace(raw_moves, "\n", "")>> do
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case char do
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"^" -> fn {x, y} -> {x, y - 1} end
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"v" -> fn {x, y} -> {x, y + 1} end
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"<" -> fn {x, y} -> {x - 1, y} end
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">" -> fn {x, y} -> {x + 1, y} end
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end
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end
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{map, robot, moves}
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else
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_ -> :error
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end
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end
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#######################
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# HERE BE BOILERPLATE #
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#######################
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def run do
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case input() do
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:error -> print_usage()
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input -> run_parts_with_timer(input)
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end
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end
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defp run_parts_with_timer(input) do
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run_with_timer(1, fn -> part1(input) end)
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run_with_timer(2, fn -> part2(input) end)
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end
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defp run_with_timer(part, fun) do
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{time, result} = :timer.tc(fun)
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IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
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IO.puts("#{inspect(result)}\n")
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end
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defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
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defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
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defp format_time(μsec), do: "#{μsec / 1_000_000}s"
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defp print_usage do
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IO.puts("Usage: elixir day15.exs input_filename")
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end
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end
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Day15.run()
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