> 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/r/run-length_encoding.md).

# Run-length encoding

Note that Raku regexes don't care about unquoted whitespace, and that backrefs count from 0, not from 1.

```perl
sub encode($str) { $str.subst(/(.) $0*/, { $/.chars ~ $0 }, :g) }

sub decode($str) { $str.subst(/(\d+) (.)/, { $1 x $0 }, :g) }

my $e = encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW');
say $e;
say decode($e);
```

Output:

```
12W1B12W3B24W1B14W 
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
```