Day5a.rb

lines = $<.map do |l|
  l =~ /(\d+),(\d+) -> (\d+),(\d+)/
  [[$1.to_i, $2.to_i], [$3.to_i, $4.to_i]]
end

map = Hash.new(0)

lines.each do |(x1, y1), (x2, y2)|
  if x1 == x2
    x = x1
    (y1..y2).each do |y|
      map[[x, y]] += 1
    end
  elsif y1 == y2
    y = y1
    (x1..x2).each do |x|
      map[[x, y]] += 1
    end
  end
end

danger = map.count {|k, v| v > 1}
print danger