找到给定编号的所有可能排列和组合。 使用 Python 的列表中的元素

Question

I need to find all possible permutations and combinations of given elements without repetition of same pairs.

For example

list = [a,b,c]

Desired output is

[(a),(b),(c),(a,b),(a,c),(b,a),(b,c),(c,a),(c,b),(a,b,c),(a,c,b),(b,a,c),(b,c,a),(c,a,b),(c,b,a)]

I tried itertools in python to get the same pairs of output but failed. Using itertools.permutations the output was

[abc,acb,bac,bca,cab,cba]

Using itertools.combinations the output was

[(), ('a',), ('b',), ('c',), ('a', 'b'), ('a', 'c'), ('b', 'c'), ('a', 'b', 'c')]

which missed the pairs like (b,a) .

Using itertools.combinations_with_replacement give repetitive elements within the pair, eg (a,a,a),(b,b,b) , which is not acceptable.

The desired output should not contain repetitive pair elements.

Answer 1

permutations allows you to specify the length of the list of permutations:

If you include the null set:

permlist = []

for i in range(len(mylist) + 1):
    permlist += itertools.permutations(mylist, i)

If you excludethe null set:

permlist = []

for i in range(len(mylist)):
    permlist += itertools.permutations(mylist, i+1)

Answer 2

answer = set()
L = ['a', 'b', 'c']
for i in range(len(L)+1):
    for c in itertools.combinations(L, i):
        for p in itertools.permutations(c):
            answer.add(p)

In [288]: answer                                                                                                                                                                                                                                                                
Out[288]: 
{(),
 ('a',),
 ('a', 'b'),
 ('a', 'b', 'c'),
 ('a', 'c'),
 ('a', 'c', 'b'),
 ('b',),
 ('b', 'a'),
 ('b', 'a', 'c'),
 ('b', 'c'),
 ('b', 'c', 'a'),
 ('c',),
 ('c', 'a'),
 ('c', 'a', 'b'),
 ('c', 'b'),
 ('c', 'b', 'a')}