「跳針跳針跳針叫我姐姐」排成一列，「跳」與「針」不相鄰的排列數有多少種？

Python Code：

import itertools

w=['a','a','a','b','b','b','c','d','e','e']

num=list(set(itertools.permutations(w))) #排列並去除相同元素

other=[]

for i in range(len(num)):

    for j in range(len(num[0])-1):

        if (num[i][j]=='a' and num[i][j+1]=='b') or \

            (num[i][j]=='b' and num[i][j+1]=='a'):

                other.append((num[i]))

ans=set(num)-set(other)

print(ans)

print(len(ans))

答案：4080種