AdventOfCode/2018/day11/day11.exs

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Elixir
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2021-12-26 13:10:19 +00:00
defmodule Day11 do
@serial 7511
@size 300
def hundreds(lvl) when lvl < 100, do: 0
def hundreds(lvl) do
[_units, _tens, hundreds | _] = Integer.digits(lvl) |> Enum.reverse()
hundreds
end
def power_level(x, y, serial) do
rack_id = x + 10
rack_id |> Kernel.*(y) |> Kernel.+(serial) |> Kernel.*(rack_id) |> hundreds() |> Kernel.-(5)
end
def grid(serial \\ @serial) do
for x <- 1..@size, y <- 1..@size, into: %{} do
{{x, y}, power_level(x, y, serial)}
end
end
def total_power(x, y, grid) do
for x <- x..(x + 2), y <- y..(y + 2) do
grid[{x, y}]
end
|> Enum.sum()
end
def find_largest_3x3(grid) do
for x <- 1..(@size - 2), y <- 1..(@size - 2) do
{{x, y}, total_power(x, y, grid)}
end
|> Enum.max_by(fn {_, power} -> power end)
end
def part1 do
{{x, y}, power} = grid() |> find_largest_3x3()
"#{x},#{y} (total power #{power})"
end
# Entry point
def largest_total_power_at(x, y, grid) do
size = 1
power = grid[{x, y}]
largest_total_power_at(x, y, grid, size, power, size, power)
end
# Terminating condition, square size has reached the edge of the grid
def largest_total_power_at(x, y, _grid, size, _power, max_size, max_power)
when x + size > @size or y + size > @size do
{x, y, max_size, max_power}
end
# Calculate extra power for square of size + 1 and take the max of the two
def largest_total_power_at(x, y, grid, size, power, max_size, max_power) do
new_x = x + size
new_y = y + size
new_row = for row_x <- x..new_x, do: grid[{row_x, new_y}]
# Minus 1 to avoid counting the corner twice
new_col = for col_y <- y..(new_y - 1), do: grid[{new_x, col_y}]
new_power = Enum.sum([power | new_row ++ new_col])
new_size = size + 1
{max_size, max_power} =
if new_power > max_power do
{new_size, new_power}
else
{max_size, max_power}
end
largest_total_power_at(x, y, grid, new_size, new_power, max_size, max_power)
end
# Still very slow, managed to avoid recalculating larger squares, but still recalculates
# smaller squares that are a subset of a larger square we already calculated.
# Could fix it, but 300x300 completes in a few mins.. maybe will come back to this
# I Wonder if replacing all the comprehensions with reduce would have a strong effect
def part2 do
grid = grid()
{x, y, size, power} =
for x <- 1..@size, IO.inspect(301 - x), y <- 1..@size do
largest_total_power_at(x, y, grid)
end
|> Enum.max_by(fn {_x, _y, _size, power} -> power end)
"Part 2 Answer: #{x},#{y},#{size} (power: #{power})"
end
end
IO.puts(Day11.part1())
IO.puts(Day11.part2())