Learn to Program, 2nd Edition

Exercises from Chapter 13

Extend the Built-in Classes

How you could do it:

class Array
  def shuffle
    arr = self
    #  Now we can just copy the old shuffle method.
    shuf = []
    while arr.length > 0
      # Randomly pick one element of the array.
      rand_index = rand(arr.length)
      # Now go through each item in the array,
      # putting them all into new_arr except for
      # the randomly chosen one, which goes into
      # shuf.
      curr_index = 0
      new_arr = []
      arr.each do |item|
        if curr_index == rand_index
          shuf.push item
        else
          new_arr.push item
        end
        curr_index = curr_index + 1
      end
      # Replace the original array with the new,
      # smaller array.
      arr = new_arr
    end
    shuf
  end
end
class Integer
  def factorial
    if self <= 1
      1
    else
 self * (self-1).factorial ...