> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/perl6-rosettacode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/perl6-rosettacode/programming_tasks/c/combinations.md).

# Combinations

There actually is a builtin:

```perl
.say for combinations(5,3);
```

#### Output:

```
(0 1 2)
(0 1 3)
(0 1 4)
(0 2 3)
(0 2 4)
(0 3 4)
(1 2 3)
(1 2 4)
(1 3 4)
(2 3 4)
```

Here is an iterative routine with the same output:

```perl
sub combinations(Int $n, Int $k) {
    return ([],) unless $k;
    return if $k > $n || $n <= 0;
    my @c = ^$k;
    gather loop {
      take [@c];
      next if @c[$k-1]++ < $n-1;
      my $i = $k-2;
      $i-- while $i >= 0 && @c[$i] >= $n-($k-$i);
      last if $i < 0;
      @c[$i]++;
      while ++$i < $k { @c[$i] = @c[$i-1] + 1; }
    }
}
.say for combinations(5,3);
```