逆序对个数求解用python怎么实现
时间: 2023-05-22 18:03:15 浏览: 50
逆序对个数可以通过归并排序实现,具体代码如下:
def merge(arr, l, m, r):
n1 = m - l + 1
n2 = r - m
L = [0] * (n1)
R = [0] * (n2)
for i in range(0, n1):
L[i] = arr[l + i]
for j in range(0, n2):
R[j] = arr[m + 1 + j]
i = 0
j = 0
k = l
count = 0
while i < n1 and j < n2:
if L[i] <= R[j]:
arr[k] = L[i]
i += 1
else:
arr[k] = R[j]
j += 1
count += (n1-i)
k += 1
while i < n1:
arr[k] = L[i]
i += 1
k += 1
while j < n2:
arr[k] = R[j]
j += 1
k += 1
return count
def mergeSort(arr,l,r):
count = 0
if l < r:
m = (l+(r-1))//2
count += mergeSort(arr, l, m)
count += mergeSort(arr, m+1, r)
count += merge(arr, l, m, r)
return count
arr = [1, 20, 6, 4, 5]
n = len(arr)
result = mergeSort(arr, 0, n-1)
print("逆序对的个数为:",result)
请注意,以上代码语言为 Python。
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