Day5b.rb

def range(i, j)
  return (i..j).each if i <= j
  Enumerator.new do |y|
    loop do
      y << i
      break if i == j
      i -= 1
    end
  end
end

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

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