我编写了这段代码,以获取使用的反转次数merge_sort
,但未获得正确的输出。有人可以告诉我为什么输出错误吗?
def merge(B,C): # B,C are sorted
D = list()
count = 0
# empty list to get the merged list
while (B != []) and (C != []): # breaks if any one of B or C becomes empty
b = B[0] # to get first element of B
print("b",b)
c = C[0] # to get first element of C
print("c",c)
if b<=c:
B.remove(b) # if b<c remove b from B and add to D
D.append(b)
else:
C.remove(c) # if b>c remove c from C and add to D
D.append(c)
count += 1
print("count_in_merge",count)
# now if either one of B or C has become empty so while loop is exited
# so we can add remaining elements of B and C as it is to D as they are
# already sorted
if B != []:
for i in B:
D.append(i)
if C != []:
for i in C:
D.append(i)
return D, count
def sort_and_num(A):
if len(A) == 1:
return A,0
m = len(A) // 2
B,count_b = sort_and_num(A[0:m])
C,count_c = sort_and_num(A[m:])
A_,count = merge(B,C)
count += (count_b + count_c)
return A_, count
当我跑步时:
A = [ 9, 8 ,7, 3, 2, 1]
A_,c = sort_and_num(A)
print(A_,c)
输出为:
[1, 2, 3, 7, 8, 9] 9
但是输出应该是
[1, 2, 3, 7, 8, 9] 15
另一方面,如果我输入:
A = [3,1,2,4]
A_, count = sort_and_num(A)
print(A_, count)
输出为:
[1,2,3,4 ] 3
哪个是对的。哪里出问题了?
您的代码中存在一些问题:
pop()
,而不是remove()
C
就是len(B)
,不是1
。sort_and_num
还应该测试一个空列表,并返回一个计数为0的列表。这是修改后的版本:
def merge(B, count_b, C, count_c): # B,C are sorted
D = []
count = count_b + count_c
# empty list to get the merged list
while (B != []) and (C != []): # breaks if any one of B or C becomes empty
if B[0] <= C[0]:
D.append(B.pop()) # if b<=c remove b from B and add it to D
else:
D.append(C.pop()) # if b>c remove c from C and add it to D
count += len(B) # moving c before all remaining elements of B
# now if either one of B or C has become empty so while loop is exited
# so we can add remaining elements of B and C as it is to D as they are
# already sorted
for i in B:
D.append(i)
for i in C:
D.append(i)
return D, count
def sort_and_num(A):
if len(A) <= 1:
return A,0
m = len(A) // 2
B,count_b = sort_and_num(A[:m])
C,count_c = sort_and_num(A[m:])
return merge(B, count_b, C, count_c)
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