|
| 1 | +defmodule AdventOfCode.Y2020.Day17 do |
| 2 | + @moduledoc """ |
| 3 | + --- Day 17: Conway Cubes --- |
| 4 | + Problem Link: https://adventofcode.com/2020/day/17 |
| 5 | + Difficulty: m |
| 6 | + Tags: simulation game-of-life infinite-grid |
| 7 | + """ |
| 8 | + alias AdventOfCode.Helpers.{InputReader, Transformers} |
| 9 | + |
| 10 | + def input, do: InputReader.read_from_file(2020, 17) |
| 11 | + |
| 12 | + def run(input \\ input()) do |
| 13 | + initial = parse(input) |
| 14 | + {solve(initial, 3), solve(initial, 4)} |
| 15 | + end |
| 16 | + |
| 17 | + defp solve(initial, dims) do |
| 18 | + state = |
| 19 | + initial |
| 20 | + |> Enum.map(fn {x, y} -> |
| 21 | + if dims == 3, do: {x, y, 0}, else: {x, y, 0, 0} |
| 22 | + end) |
| 23 | + |> MapSet.new() |
| 24 | + |
| 25 | + Enum.reduce(1..6, state, fn _, acc -> step(acc, dims) end) |
| 26 | + |> MapSet.size() |
| 27 | + end |
| 28 | + |
| 29 | + defp step(active, dims) do |
| 30 | + neighbor_counts = |
| 31 | + active |
| 32 | + |> Enum.reduce(%{}, fn pos, counts -> |
| 33 | + get_neighbors(pos, dims) |
| 34 | + |> Enum.reduce(counts, fn n, acc -> Map.update(acc, n, 1, &(&1 + 1)) end) |
| 35 | + end) |
| 36 | + |
| 37 | + for {pos, count} <- neighbor_counts, |
| 38 | + count == 3 or (count == 2 and MapSet.member?(active, pos)), |
| 39 | + into: MapSet.new() do |
| 40 | + pos |
| 41 | + end |
| 42 | + end |
| 43 | + |
| 44 | + defp get_neighbors({x, y, z}, 3) do |
| 45 | + for dx <- -1..1, dy <- -1..1, dz <- -1..1, {dx, dy, dz} != {0, 0, 0} do |
| 46 | + {x + dx, y + dy, z + dz} |
| 47 | + end |
| 48 | + end |
| 49 | + |
| 50 | + defp get_neighbors({x, y, z, w}, 4) do |
| 51 | + for dx <- -1..1, dy <- -1..1, dz <- -1..1, dw <- -1..1, {dx, dy, dz, dw} != {0, 0, 0, 0} do |
| 52 | + {x + dx, y + dy, z + dz, w + dw} |
| 53 | + end |
| 54 | + end |
| 55 | + |
| 56 | + def parse(data \\ input()) do |
| 57 | + data |
| 58 | + |> Transformers.lines() |
| 59 | + |> Enum.with_index() |
| 60 | + |> Enum.flat_map(fn {line, y} -> |
| 61 | + line |
| 62 | + |> String.graphemes() |
| 63 | + |> Enum.with_index() |
| 64 | + |> Enum.filter(fn {char, _} -> char == "#" end) |
| 65 | + |> Enum.map(fn {_, x} -> {x, y} end) |
| 66 | + end) |
| 67 | + end |
| 68 | +end |
0 commit comments