next_permutation.pl

#!/usr/bin/env perl
use v5.18;

sub next_permutation {
    my $p = shift;
    my $l = @$p;
    my $i;
    for ($i = $l-1; $i > 0; $i--) {
        last if $p->[$i] > $p->[$i-1];
    }
    $i--;
    return 0 if $i < 0;

    my @q = @$p;
    my $j = $i+1;
    for ($i+1 ... $l-1) {
        next unless $p->[$_] > $p->[$i];
        $j = $_ if $p->[$_] < $p->[$j];
    }

    @q[$i, $j] = @$p[$j, $i];
    @q[$i+1 ... $l-1] = reverse( @q[$i+1 ... $l-1] );

    @$p = @q;
    return 1;
}

my @p = (0, 1, 2, 3, 4);
say join " ", @p;

while(1) {
    if ( next_permutation(\@p) ) {
        say join " ", @p;
    } else {
        last;
    }
}