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Re^2: generating permutations

by Anonymous Monk
on Mar 29, 2017 at 20:36 UTC ( [id://1186434] : note . print w/replies, xml ) Need Help??

in reply to Re: generating permutations
in thread generating permutations

Thanks, again. With a few extra print statements, I am able to see exactly what it is doing.

A quick (I hope) follow up. How would I do a more general list - say all the permutations of (apple, banana, orange), or numbers that go into double digits?

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Re^3: generating permutations
by BrowserUk (Patriarch) on Mar 29, 2017 at 21:21 UTC

    Try this. It's a re-casting of the Python algorithm to operate on arrays:

    #! perl -slw use strict; sub permute3 { my( $in, $pre ) = ( @_, [] ); return print join '-', @$pre unless @$in; permute3( [ @{ $in }[ 0 .. $_-1, $_+1 .. $#$in ] ], [ @$pre, $in->[ $_ ] ] ) for 0 .. $#$in; } permute3( [ qw[ apple banana orange ] ] );; __END__ C:\test>junk36 apple-banana-orange apple-orange-banana banana-apple-orange banana-orange-apple orange-apple-banana orange-banana-apple

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Re^3: generating permutations
by tybalt89 (Monsignor) on Mar 31, 2017 at 22:35 UTC

    Here's a version that uses a separate array to mark when a item is used instead of building and destroying anon arrays.

    #!/usr/bin/perl # use strict; use warnings; my @items = qw( apple banana orange ); my @used; sub permute { @_ == @items and return print "@_\n"; $used[$_]++ || permute(@_, $items[$_]), $used[$_]-- for 0 .. $#items +; } permute();