Question

I am in need of an algorithm (preferably Java) that can find the combination of a sequence of numbers. Here is an example that I would like to achieve.

Suppose the given sequence of number is: 1 2 3

I am expecting the output to be:

1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1
1 2
1 3
2 1
2 3
3 1
3 2
1
2
3

I remember I’ve searched this before here in stackover flow and I found the answer but that was like 2 years ago. Now I’m doing a project and I needed that algorithm again.

Answer 1

Python is often referred to as “batteries included“, and this is for a good reason.

permutations is available in the itertools module.

>>> from itertools import permutations
>>>
>>> l = [1,2,3]
>>> all_permutations = []
>>> for i in range(2, len(l) + 1):
...     all_permutations.extend(list(permutations(l, i)))
...
>>> all_permutations.extend(l)
>>> all_permutations
[(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2), (1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1), 1, 2, 3]