python 数据结构之归并排序

def merger_sort(alist):
    if len(alist) <= 1 :
        return alist
    num=int(len(alist)/2)
    left=merger_sort(alist[:num])  
    right=merger_sort(alist[num:])   #分前后两个顺序
    return merger(left,right)

def merger(left,right):
    l,r=0,0
    result = []  # 存放结果
    while l < len(left) and r < len(right):
        if left[l]<right[r]:
            result.append(left[l])
            l+=1
        else :
            result.append(right[r])
            r+=1
    result+=left[l:]
    result+=right[r:]
    return result

alist=[0,1,45,86,9,3,10,4,2]
b=merger_sort(alist)
print(b)