python实现归并排序 --算法导论

def merge(A, p, q, r):
    n1 = q - p + 1
    n2 = r - q 
    L = list(range(n1 + 1))
    R = list(range(n2 + 1))
    for i in range(0, n1):
        L[i] = A[p + i]
    for j in range(0, n2):
        R[j] = A[q + j + 1]
    L[n1] = 10000 #这里可以使用无穷大/也可以使用一个比数组最大的元素大的值
    R[n2] = 10000
    i = 0
    j = 0
    for k in range(p, r+1):         
        if L[i] <= R[j]:
            A[k] = L[i]
            i = i + 1
        else:
            A[k] = R[j]
            j = j + 1
def mergesort(A, p, r):
    if p < r:
        q = int((p+(r-1))/2)
        mergesort(A,p,q)
        mergesort(A,q+1,r)
        merge(A,p,q,r) 
        return A 
A = []   
n = int(input("请输入你需要排序的数组的长度:"))  
for i in range(0, n):
    B = int(input("请依次输入你需要排序的数组元素:"))
    A.append(B)
print(mergesort(A, 0, len(A)-1))