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 another way to implement quicksort -- as a newbie I think it's easier to understand -- hope it helps someone :) in this implementation the pivot is always the last element in the array -- I'm following the Khan Academy course and that's where I got the inspiration from

def quick_sort(array, beg_index, end_index)
  if beg_index < end_index
    pivot_index = partition(array, beg_index, end_index)
    quick_sort(array, beg_index, pivot_index -1)
    quick_sort(array, pivot_index + 1, end_index)
  end
  array
end

#returns an index of where the pivot ends up
def partition(array, beg_index, end_index)
  #current_index starts the subarray with larger numbers than the pivot
  current_index = beg_index
  i = beg_index
  while i < end_index do
    if array[i] <= array[end_index]
      swap(array, i, current_index)
      current_index += 1
    end
    i += 1
  end
  #after this swap all of the elements before the pivot will be smaller and
  #after the pivot larger
  swap(array, end_index, current_index)
  current_index
end

def swap(array, first_element, second_element)
  temp = array[first_element]
  array[first_element] = array[second_element]
  array[second_element] = temp
end

puts quick_sort([2,3,1,5],0,3).inspect #will return [1, 2, 3, 5]