[Jprogramming] restricting permutations

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ssmb=:+./@E.

l21=.-.1 1 ssmb"1+./"2]1 2=/"1 n=.perm 4

l30=.-.1 1 ssmb"1+./"2]0 3=/"1 n

n#~l30*.l21

0 1 3 2

0 2 3 1

1 0 2 3

1 3 2 0

2 0 1 3

2 3 1 0

3 1 0 2

3 2 0 1


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On Mon, May 25, 2020 at 6:48 AM Brian Schott <schott.brian at gmail.com> wrote:

> I want all permutations of  i. 4 for which 0 and 3 cannot be adjacent, nor
> can 1 and 2. My idea is to create a as follows to describe my situation.
>
>    ]a =. 0 1 1 0,:i. 4
>
> 0 1 1 0
>
> 0 1 2 3
>
>
> Next I created b and rotations on b to list the possibilities I can think
> of. So I can think of 6 permutations. Are there more and is there a better
> way to generate the real qualifying permutations?
>    ]b =. 0 1 3 2 ,:1 0 2 3
> 0 1 3 2
> 1 0 2 3
>    1|."1 b
> 1 3 2 0
> 0 2 3 1
>    _1|."1 b
> 2 0 1 3
> 3 1 0 2
> --
> (B=)
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