array.rb

class Array
  def same_structure_as(b)
    return false unless b.is_a?(Array) && self.is_a?(Array)
  
    c = self.each_with_object([]) do |c,d|
      if c.is_a?(Array)
        d << c.length
      else
        d << 1
      end
    end
    
    e = b.each_with_object([]) do |c,d|
      if c.is_a?(Array)
        d << c.length
      else
        d << 1
      end
    end
    
    c == e && depth(self) == depth(b)
  end
  
  def depth(a)
    return 0 unless a.is_a?(Array)
    return 1 + depth(a[0])
  end
end

best.rb

class Array

  def same_structure_as(a)
    return false if self.class!=a.class || size!=a.size 
    a.each_index { |i| return false if self[i].class==Array && !self[i].same_structure_as(a[i]) }
    true
  end
  
end