Advent of Code 2021 day 07

Setup

Mix.install([
  {:kino, github: "livebook-dev/kino"}
])

input = Kino.Input.textarea("Please paste your input file:")

crabs =
  input
  |> Kino.Input.read()
  |> String.split([",", "\n"], trim: true)
  |> Enum.map(&String.to_integer/1)

Part 1

median =
  crabs
  |> Enum.sort()
  |> Enum.at(crabs |> length() |> div(2))

deviations =
  crabs
  |> Enum.map(&((&1 - median) |> abs()))
  |> Enum.sum()

Part 2

defmodule Day7 do
  def step_sum(i, j) do
    n = abs(j - i)
    (n + 1) * n / 2
  end
end

mean =
  crabs
  |> Enum.sum()
  |> Kernel./(length(crabs))
  |> IO.inspect(label: :mean)

floor(mean)..ceil(mean)
|> Enum.map(fn i ->
  crabs
  |> Enum.map(&Day7.step_sum(i, &1))
  |> Enum.sum()
end)
|> Enum.min()
|> trunc()

# deviations =
#   crabs
#   |> Enum.map(&(&1 - mean) |> abs())
#   |> Enum.map(&Day7.step_sum/1)
#   |> Enum.sum()