Ruby快速排序：堆栈级别太深（SystemStackError）

def quick_sort(list)
  return list if list.size <= 1
  p = list.sample
  left, right = list.partition{|elmt| elmt <= p}
  quick_sort(left) + quick_sort(right)
end

a = [9,8,7,6,5,0,6]
b = quick_sort(a)
puts b
def quick_sort(list)
  return list if list.size