Fetch by category from Rubeque. You need the rest-client gem

rubeque.rb

#!/usr/bin/env ruby                                                                
require 'rest-client'                                                              
require 'json'                                                                     
                                                                                   
class Rubeque                                                                      
  def initialize                                                                   
    @questions = categorize                                                        
  end                                                                              
                                                                                   
  def categories                                                                   
    puts @questions.keys                                                           
  end                                                                              
                                                                                   
  def questions_for(category)                                                      
    @questions[category].sort_by {|q| q["difficulty"].to_i}.each do |question|  
      puts "Difficulty #{question["difficulty"]}"                                  
      puts question["instructions"]                                                
      puts question["code"]                                                        
      puts "-" * 40                                                                
      puts                                                                         
    end                                                                            
  end                                                                              
                                                                                   
  private                                                                          
                                                                                   
  def categorize                                                                   
    result = JSON.load(RestClient.get("http://www.rubeque.com/problems.json"))  
    questions = Hash.new {|k,v| k[v] = [] }                                        
                                                                                   
    result.each_with_object(questions) do |r|                                      
      if r["tags"]                                                                 
        r["tags"].each do |t|                                                      
          questions[t["name"].strip] << r                                          
        end                                                                        
      else                                                                         
        questions["untagged"] << r                                                 
      end                                                                          
    end                                                                            
  end                                                                              
end                                                                                
                                                                                   
rbq = Rubeque.new                                                                  
rbq.questions_for 'enumerables'                                                    
rbq.categories