defmodule Aoc.Y2020.D9 do
use Aoc.Boilerplate,
transform: fn raw ->
raw
|> String.split("\n")
|> Enum.map(&String.to_integer/1)
end
@preamble 25
defguard sums_to_needed_sum(first, second, needed_sum) when first + second == needed_sum
def part1(input \\ processed()) do
input
|> Enum.chunk_every(@preamble + 1, 1, :discard)
|> Enum.find_value(fn chunk ->
{last, chunk} = List.pop_at(chunk, -1)
if valid?(chunk, last), do: false, else: last
end)
end
def part2(input \\ processed()) do
invalid_number = input |> part1()
Stream.iterate(2, &(&1 + 1))
|> Enum.find_value(fn chunk_size ->
input
|> Enum.chunk_every(chunk_size, 1, :discard)
|> Enum.find_value(fn chunk ->
sum = Enum.sum(chunk)
if sum == invalid_number do
{min, max} = Enum.min_max(chunk)
min + max
end
end)
end)
end
def valid?(list, next) do
get_two(list, next) != nil
end
def get_two([_first | rest] = list, needed_sum) do
get_two(list, rest, needed_sum)
end
def get_two([], _needed_sum), do: nil
def get_two(list, remainder, needed_sum) when length(list) == 1,
do: get_two(remainder, needed_sum)
def get_two([first | [second | _rest]], _remainder, needed_sum)
when sums_to_needed_sum(first, second, needed_sum) do
{first, second}
end
def get_two([first | [_second | rest]], remainder, needed_sum) do
get_two([first | rest], remainder, needed_sum)
end
end
egze
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adolfont
i tried something different with #AdventofCode2020 Day 9. I did not solve it. I tried to understand and refactor a Day 9 solution from somebody else.
The code (from Martin Gausby and @LostKobrakai) is rewritten or commented here: https://github.com/Introduction-to-Functional-Programming/simple_exercises/blob/main/adolfont/adventofcode/2020/day_09/lib/day09.ex.
I learned a lot.
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