学步园

题目地址：http://hero.pongo.cn/Question/Details?ID=58&ExamID=56

  def initialize(array)
    @array = array
  end

  def largest_rectangle_area
    max_area = 0
    @array.each_index do |i|
      right_blocks = @array[(i + 1)...@array.count]
      right_position = (right_blocks.index{|block_height| block_height < @array[i]} || right_blocks.count) + i
      left_blocks = @array[0...i]
      if left_position = left_blocks.rindex{|block_height| block_height < @array[i]} 
        left_position += 1
      else
        left_position = 0
      end
      area_width = right_position - left_position + 1 
      area = area_width * @array[i]
      max_area = area if area > max_area
    end
    max_area
  end
end

describe Histogram do
  it "should be 10 if height array is [2,1,5,6,2,3] " do
    Histogram.new([2,1,5,6,2,3]).largest_rectangle_area.should == 10
  end

  it "should be 8 if height array is [2,2,2,2] " do
    Histogram.new([2, 2, 2, 2]).largest_rectangle_area.should == 8
  end

  it "should be 9 if height array is [1,2,3,4, 5] " do
    Histogram.new([1,2,3,4, 5]).largest_rectangle_area.should == 9
  end

end