day14.rb

require 'byebug'
if ARGV.empty?
  input = <<~INPUT
  498,4 -> 498,6 -> 496,6
  503,4 -> 502,4 -> 502,9 -> 494,9
  INPUT
else
  input = File.read(ARGV.first, chomp: true)
end

lines = input
  .split("\n")
  .map {_1.split(" -> ")}
  .map do |line|
    line.map do |point|
      point
        .split(",")
        .map(&:to_i)
    end
      .each_cons(2)
      .to_a
  end

MARGIN = 500

def bounds(lines)
  min_r, max_r = lines.flat_map do |line|
    line.flat_map do |segment|
      segment.map(&:first)
    end
  end.minmax
  min_c, max_c = lines.flat_map do |line|
    line.flat_map do |segment|
      segment.map(&:last)
    end
  end.minmax
  [min_r - MARGIN, max_r + MARGIN, 0, max_c + 2]
end

def lines_to_grid(lines, bounds)
  min_r, max_r, min_c, max_c = bounds
  grid = Array.new(max_c - min_c + 1) do
    Array.new(max_r - min_r + 1, ".")
  end
  lines.each do |line|
    line.each do |segment|
      start, finish = segment.sort
      start_r, start_c = start
      finish_r, finish_c = finish
      (start_r..finish_r).each do |r|
        (start_c..finish_c).each do |c|
          grid[c - min_c][r - min_r] = "#"
        end
      end
    end
  end
  grid[-1] = Array.new(max_r - min_r + 1, "#")
  grid
end

def pour_sand(bounds, grid, entry)
  min_r, max_r, min_c, max_c = bounds
  r, c = entry

  rest = false
  while !rest
    if !r.between?(min_r, max_r)
      throw :done
    end
    nc = c + 1 - min_c
    nr = r - min_r

    if grid[nc][nr] == "."
      c += 1
    elsif grid[nc][nr] == "o" || grid[nc][nr] == "#"
      # try the left
      if grid[nc][nr - 1] == "."
        r -= 1
        c += 1
        # try the right
      elsif grid[nc][nr + 1] == "."
        r += 1
        c += 1
      else
        rest = true
      end
    end
  end

  grid[c - min_c][r - min_r] = "o"
  throw :done if [r, c] == entry
  grid
end

def display(grid)
  puts
  grid.each do |row|
    puts row.join
  end
end

b = bounds(lines)
grid = lines_to_grid(lines, b)
count = 0
catch :done do
  while true
    pour_sand(b, grid, [500, 0])
    count += 1
    p count
  end
end
p count

https://youtu.be/h7W8VipzBbk