use two methods that call each other to sort penguins with quicksort in an alternating fashion

quicksort.rb

##
# This is a demonstration of a valid reason for having two methods that call each other.
# It is part of a response to a queuestion online
# https://softwareengineering.stackexchange.com/questions/376333/is-2-methods-calling-each-other-code-smell/377660#377660
#
# See a video of me making this at https://youtu.be/YugJV21W91A
#
# we are using recursion to implement quicksort.
# The sort is implemented two slightly different ways
# and each way calls the other to do the next level down the tree.
#
# imagine we're sorting penguins by height

def quicksort_pop(penguins)
  return penguins if penguins.length <= 1
  pivot = penguins.pop
  left = []
  right = []
  while penguins.any?
    penguin = penguins.pop
    (penguin < pivot) ? left << penguin : right << penguin
  end
  quicksort_shift(left) + [pivot] + quicksort_shift(right)
end

def quicksort_shift(penguins)
  return penguins if penguins.length <= 1
  pivot = penguins.shift
  left = []
  right = []
  while penguins.any?
    penguin = penguins.shift
    (penguin < pivot) ? left << penguin : right << penguin
  end
  quicksort_pop(left) + [pivot] + quicksort_pop(right)
end

def get_penguin_heights
  puts 'Those are nice penguins'
  puts 'Please tell me each of their heights (comma seperated ints)...'
  heights = gets.chomp
  heights.split(',').map{ |height| height.to_i }
end

def give_sorted_penguins(penguins)
  puts "thank you! That's an awesome collection of penguins!"
  puts "BTW, I put them in height order for you:"
  puts penguins
  favourite_index = Random.rand(penguins.length)
  puts "My favourite is the one that's #{penguins[favourite_index]}cm tall,"
  puts 'can I keep him?'
end

init_penguins = get_penguin_heights
sorted_penguins = quicksort_pop(init_penguins)
give_sorted_penguins(sorted_penguins)