Quick Sort in Ruby language

Question

I am trying to implement Quick sort in ruby but stuck in how to call recursively after the first partition of pivot. Please help me to understand on how to proceed and also

Answer 1

Here is a (very) naive quicksort implementation, based on Wikipedia's simple-quicksort pseudocode:

def quicksort(array) #takes an array of integers as an argument

You need a base case, otherwise your recursive calls never terminate

if array.length <= 1
  return array

Now pick a pivot:

else
  pivot = array.sample
  array.delete_at(array.index(pivot)) # remove the pivot
  #puts "Picked pivot of: #{pivot}"
  less = []
  greater = []

Loop through the array, comparing items to pivot and collecting them into less and greater arrays.

  array.each do |x|
    if x <= pivot
      less << x
    else
      greater << x
    end
  end

Now, recursively call quicksort() on your less and greater arrays.

  sorted_array = []
  sorted_array << self.quicksort(less)
  sorted_array << pivot
  sorted_array << self.quicksort(greater)

Return the sorted_array and you're done.

  # using Array.flatten to remove subarrays
  sorted_array.flatten!

You can test it with

qs = QuickSort.new

puts qs.quicksort([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5] # true
puts qs.quicksort([5]) == [5] # true
puts qs.quicksort([5, -5, 11, 0, 3]) == [-5, 0, 3, 5, 11] # true
puts qs.quicksort([5, -5, 11, 0, 3]) == [5, -5, 11, 0, 3] # false