Quick sort

sort.rb

def quick_sort(list)
  qsort_helper(list).flatten
end
 
def qsort_helper(list)
  return [] if list.empty?
 
  number        = list.sample
  lower, higher = list.partition { |n| n < number }
 
  higher.delete_at(higher.index(number))
 
  [qsort_helper(lower), number, qsort_helper(higher)]
end
 
p quick_sort [3, 7, 2, 1, 8, 12]
 
# [1, 2, 3, 7, 8, 12]

use the sort & the sort_by methods to sort your arrays & hashes in different ways.

hash = {coconut: 200, orange: 50, bacon: 100}
 
hash.sort_by(&:last)
 
# [[:orange, 50], [:bacon, 100], [:coconut, 200]] 

music = %w(21.mp3 10.mp3 5.mp3 40.mp3) 

music.sort
 
# ["10.mp3", "21.mp3", "40.mp3", "5.mp3"] 
music.sort_by { |s| s.scan(/\d+/).first.to_i }
 
# ["5.mp3", "10.mp3", "21.mp3", "40.mp3"]

Ruby Constant 
ABC = 1  correct but if we try 
def the_method
  ABC = 1
end
Notice that you can’t define constants inside a method.
You will get this cryptic error message:
So just define your constants outside methods, typically we want to have constant definitions at the top of your class so they are clearly visible.

class RubyBlog
  URL    = "blackbytes.info"
  AUTHOR = "Jesus Castello"
end
p RubyBlog::AUTHOR 
 Ruby constants can change But you will see this warning message
 to avoid this AUTHOR = "HEY RUBY".freeze
 
AUTHOR << "o"
# RuntimeError: can't modify frozen String

nested calss 
class A
  FOO = 1
end
 
class A::B
  class C
    puts FOO
  end
end
Notice the A::B notation here, which we tried to use as a shortcut. But the problem is that class C won’t have access to FOO directly.
For that reason you want to stick to this kind of nesting: 
class A
  FOO = 1
end
 
class A
  class B
    class C
      puts FOO
    end
  end
end
In the first example you can still do ::A::FOO to access the constant, but if the class name changes then you will get an error.

This ::A::FOO syntax works because it tells Ruby to look in the top-level scope, where constants like Array & String are defined