defmodule Day5 do
def read_file(path) do
{:ok, contents} = File.read(path)
String.split(contents, "\n\n", trim: true)
end
def create_almanac(sections) do
almanac_object = %{
seed_numbers: nil,
seed_ranges: [],
to_soil: nil,
to_fertilizer: nil,
to_water: nil,
to_light: nil,
to_temperature: nil,
to_humidity: nil,
to_location: nil,
}
almanac = Enum.with_index(sections)
|> Enum.reduce(almanac_object, fn section_tuple, updated_almanac ->
{section, index} = section_tuple
if index == 0 do
seed_numbers = Regex.scan(~r/[\d]+/, section)
|> Enum.map(fn seed_number_list ->
String.to_integer(Enum.at(seed_number_list, 0))
end)
Map.replace(updated_almanac, :seed_numbers, seed_numbers)
else
section_name = Enum.at(Enum.at(Regex.scan(~r/to-[\w]+/, section), 0), 0)
section_name = section_name
|> String.replace("-", "_")
section_name = String.to_atom(section_name)
section_numbers =
Enum.drop(String.split(section, "\n", trim: true), 1)
maps =
section_numbers
|> Enum.map(fn numbers ->
numbers =
String.split(numbers)
|> Enum.map(&String.to_integer/1)
{Enum.at(numbers, 0), Enum.at(numbers, 1), Enum.at(numbers, 2)}
end)
Map.replace(updated_almanac, section_name, maps)
end
end)
extract_seed_range_info(almanac)
end
def get_destination_number(source_number, maps) do
maps
|> Enum.reduce_while(source_number, fn map, acc ->
{dest_range_start, source_range_start, range_length} = map
if acc >= source_range_start &&
acc <= source_range_start + range_length do
{:halt, dest_range_start + acc - source_range_start}
else
{:cont, acc}
end
end)
end
def get_destination(almanac, dest_category, seeds) do
categories = ["soil", "fertilizer", "water", "light", "temperature", "humidity", "location"]
Enum.map(seeds, fn seed ->
Enum.reduce_while(categories, seed, fn category, dest_number ->
current_map = Map.get(almanac, String.to_atom("to_#{category}"))
dest_number = get_destination_number(dest_number, current_map)
if category == dest_category do
{:halt, dest_number}
else
{:cont, dest_number}
end
end)
end)
end
def extract_seed_range_info(almanac) do
Enum.chunk_every(almanac.seed_numbers, 2)
|> Enum.reduce(almanac, fn range_pair, updated_almanac ->
Map.put(updated_almanac, :seed_ranges, [{Enum.at(range_pair, 0), Enum.at(range_pair, 1)} | updated_almanac.seed_ranges])
end)
end
def solve_part_2(path) do
almanac =
read_file(path)
|> create_almanac()
locations = List.flatten(almanac.seed_ranges
|> Enum.reduce([], fn range_tuple, locations ->
{range_start, range_length} = range_tuple
[get_destination(almanac, "location", range_start..(range_length + range_start)) | locations]
end))
Enum.min(locations)
end
end
