ordered subsequence with possible duplicates

.pl

sub contiguous_subsequences {
    my ($little_set, $big_set) = @_;

    my $little_set_size = @$little_set;
    my $big_set_size    = @$big_set;

    my @matches;

    my ($i, $j) = (0, 0); # sequence indices
    my $k = 0; # matches found
    my $p = 0; # initial big set position
    my $f = 0; # failed to find match

    while ($i < $little_set_size && $j < $big_set_size) {
        if ($little_set->[$i] eq $big_set->[$j]) {
            $k++;   # We match
            $j++;   # Move to the next element in the big_set
            $f = 0; # reset failure flag
        }
        else {
            $f++; # we failed to match
        }
        $i++;  # Move to the next element in the little_set
        if ($f || $i >= $little_set_size) {
            push @matches, $p if $k == $little_set_size;
            $p++;    # increment the big set position
            $i = 0;  # reset the little set position
            $j = $p; # set the big set index to the big set position
            $k = 0;  # no matches seen
        }
    }

    return \@matches;
}