快速排序

## 快速排序的平均运行时间为O_{(n log n)}，在最糟糕的情况下运行时间为O_(n²)

def quick_sort(arr):
    if len(arr) < 2:
        return arr
    pivot = arr[0]
    less = [i for i in arr[1:]  if i < pivot]
    greater = [i  for i in arr[1:] if i >= pivot]
    return quick_sort(less) + [pivot] + quick_sort(greater) 

print(quick_sort([3, 5, 47, 8, 34, 2, 34, 2, 56, 5, 7, 76, 23, 4, 213, 12]))
# [2, 2, 3, 4, 5, 5, 7, 8, 12, 23, 34, 34, 47, 56, 76, 213]