python排序之归并排序

思想：先递归分解数组，再合并数组

代码:

def merge_sort(alist):
    n=len(alist)
    if n<=1:
        return alist
    mid=n//2
    left_li=merge_sort(alist[:mid])
    right_li=merge_sort(alist[mid:])
    left_pointer,right_pointer=0,0
    result=[]
    while left_pointer<len(left_li) and right_pointer<len(right_li):
        if left_li[left_pointer]<=right_li[right_pointer]:
            result.append(left_li[left_pointer])
            left_pointer+=1
        else:
            result.append(right_li[right_pointer])
            right_pointer+=1
    result+=left_li[left_pointer:]
    result+=right_li[right_pointer:]
    return result

最优时间复杂度:O(nlogn)

最差时间复杂度：O(nlogn)

稳定性：稳定