Ruby Quicksort Implementation (In-Place)

quicksort.rb

class Array
  def qsort!(low = 0, high = self.size - 1)
    return self if high <= low
    
    pivot_idx = rand(low..high)
    pivot = self[pivot_idx]
    self[pivot_idx], self[high] = self[high], pivot
    i, j = low - 1, high

    begin
      begin i += 1 end while self[i] < pivot
      begin j -= 1 end while self[j] > pivot && j > low
      self[i], self[j] = self[j], self[i] if i < j
    end while i < j

    self[high] = self[i]
    self[i] = pivot
    qsort!(low, i - 1)
    qsort!(i + 1, high)
  end

  def qsort
    dup.qsort!
  end
end