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Permutations/Derangements: Difference between revisions
→{{header|Perl 6}}
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Line 2,167:
{{works with|Rakudo|2016.10}}
<lang perl6>
sub
}
(1, 0, 1, -> $a, $b { ($++ + 2) × ($b + $a) } ... *)[$n]
sub derangements(Range $x) {▼
▲ $x.permutations.grep( *.&is-derangement )
}
▲sub prefix:<!>(Int $x) {
▲for ^9 -> $n {
▲ say "count: " ~ !$n;
}
</lang>
{{out}}
<pre>
((2 1 4 3) (2 3 4 1) (2 4 1 3) (3 1 4 2) (3 4 1 2) (3 4 2 1) (4 1 2 3) (4 3 1 2) (4 3 2 1))
!0 == 1
!1 == 0
!2 == 1
!3 == 2
!4 == 9
!5 == 44
!6 == 265
!7 == 1854
!8 == 14833
!9 == 133496
</pre>
=={{header|Phix}}==
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