gistfile1.rb

class Array
  
  def antiuniq
    
    duplicates = []
    clone = [] + self
    
    while clone.length > 0
      item = clone.pop
      duplicates.push(item) if clone.include?(item) || duplicates.include?(item)
    end
  
    return duplicates
  end
  
  def antiuniq!
    self.replace antiuniq
  end
  
end