def assert(x, y)
  raise [x, y].inspect unless x == y
end

class Solution
  def self.run(buildings)
    changes = []
    result = []
    buildings.each do |building|
      left, right, height = building
      left.upto(right) do |n|
        changes[n] = height
      end
    end
    current = nil
    changes.each_with_index do |item, index|
      next if item == current

      current = item
      result << [index, item]
    end
    result << [changes.size, 0]
    result
  end
end

assert Solution.run([[2,8,3], [4,6,5]]), [[2,3], [4,5], [7,3], [9,0]]