Advent of Code 2023 - Day 6

Sample

sample = """
Time:      7  15   30
Distance:  9  40  200
"""

"Time:      7  15   30\nDistance:  9  40  200\n"

Input

input = """
Time:        40     82     84     92
Distance:   233   1011   1110   1487
"""

"Time:        40     82     84     92\nDistance:   233   1011   1110   1487\n"

Part 1

quad = fn t, r ->
  break_even = (t - :math.sqrt(t * t - 4 * r)) / 2
  ceiling = ceil(break_even)

  if ceiling > break_even do
    ceiling
  else
    break_even + 1
  end
end

[times, records] =
  input
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    [_label, values] = String.split(line, ~r/:\s+/)
    values |> String.split(~r/\s+/) |> Enum.map(&String.to_integer/1)
  end)

races = Enum.zip(times, records)

Enum.map(races, fn {time, record} ->
  x = quad.(time, record)
  time - 2 * x + 1
end)
|> Enum.product()

3316275

Part 2

quad = fn t, r ->
  break_even = (t - :math.sqrt(t * t - 4 * r)) / 2
  ceiling = ceil(break_even)

  if ceiling > break_even do
    ceiling
  else
    break_even + 1
  end
end

[time, record] =
  input
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    [_label, values] = String.split(line, ~r/:\s+/)
    values |> String.replace(~r/\s+/, "") |> String.to_integer()
  end)

x = quad.(time, record)
time - x * 2 + 1

27102791