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How do I permute N elements of a list?

by faq_monk (Initiate)
on Oct 08, 1999 at 00:20 UTC ( #618=perlfaq nodetype: print w/ replies, xml ) Need Help??

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

Here's a little program that generates all permutations of all the words on each line of input. The algorithm embodied in the permute() function should work on any list:

    #!/usr/bin/perl -n
    # tsc-permute: permute each word of input
    permute([split], []);
    sub permute {
        my @items = @{ $_[0] };
        my @perms = @{ $_[1] };
        unless (@items) {
            print "@perms\n";
        } else {
            my(@newitems,@newperms,$i);
            foreach $i (0 .. $#items) {
                @newitems = @items;
                @newperms = @perms;
                unshift(@newperms, splice(@newitems, $i, 1));
                permute([@newitems], [@newperms]);
            }
        }
    }

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