interview coding questions

1.  what is the problem in the below code 

authors = Author.all

authors.each do |author|

puts author.name

author.books.each do |book|

puts book.name

end

end

my answer : 

[11:25 AM] dwijendra (Guest)

authors = Author.all

books = authors.map(&:books).flatten

authors.each do |author|

puts author.name

author.books.each do |book|

puts book.name

end

end

​

[11:26 AM] dwijendra (Guest)

authors = Author.includes(books:[:author]).all

books = authors.map(&:books).flatten

authors.each do |author|

puts author.name

author.books.each do |book|

puts book.name

end

end

2.  How to get the 1000 output id's ::

 user_permissions

id user_id permisssion_id

1 001 1000

2 001 1001

3 002 1000

my answer :: 

[11:33 AM] dwijendra (Guest)

user_id.map(&:permission_id).count

​

[11:35 AM] dwijendra (Guest)

user_id.select(&:permission_id).count

​

[11:36 AM] dwijendra (Guest)

user_id.select(&:permission_id).duplicate.count