# ETOOBUSY đźš€ minimal blogging for the impatient

# AoC 2021/5 - Hyperstuff

**TL;DR**

On with Advent of Code puzzle 6 from 2021: solving with hyperoperators.

Todayâ€™s puzzle was â€śeasierâ€ť from my point of view, in the sense that I had a precise idea of how to address it since the beginning. I will not show the initial solution, though, but a transformed version that gave me an occasion to look at hyperoperators.

```
sub part-all ($filename where *.IO.e) {
my (%counts);;
for $filename.IO.lines {
my ($p1, $p2) = .comb(/ \-? \d+ /).map: {[$^x, $^y]};
my $deltas = $p2 Â«-Â» $p1;
$deltas = $deltas Â«/Â» $deltasÂ».abs.max;
my $is-hv = ([*] @$deltas) == 0; # is it horizontal/vertical?
$p2 Â«+=Â» $deltas; # move one step ahead to include it too
while $p1 !~~ $p2 {
%counts<over-1>{$p1}++ if $is-hv && %counts<1>{$p1}++;
%counts<over-2>{$p1}++ if %counts<2>{$p1}++;
$p1 Â«+=Â» $deltas;
}
}
return %counts<over-1 over-2>Â».keysÂ».elems;
}
```

The idea is to sweep through the inputs and use each line, then toss it
away. The four input values are parsed via `.comb`

and arranged into two
arrays, which end up in `$p1`

and `$p2`

respectively. The `.map`

comes
handy here in providing us more than one element when we ask for them
(via the *circumflexed* variables `$^x`

and `$^y`

, which act as
indicators that the block of code passed to `map`

takes two input
parameters).

From here itâ€™s all operations on *points*, represented as arrays of two
values, thanks to the hyperoperators. Itâ€™s a bit weird that, with
some [Matlab][] background from *a lot* of time ago, I didnâ€™t catch with
these operators before. Maybe Huffman was right: in [Matlab][]
operations are upon vectors by default, and you have to put something
additional to trigger a different behaviour; here the normal behaviour
is the scalar one, and you have to put something additional to make it
different.

Anyway, the `$delta`

array eventually contains how much we should
â€śadvanceâ€ť in either coordinate to go from point `$p1`

up to point `$p2`

.
To make sure we also include the input `$p2`

, it is itself increased
once by the `$delta`

, so that we can iterate our `while`

condition upon
`$p1`

being different from `$p2`

.

A segment that is either horizontal or vertical will have one of the to
differences/increments set to 0, so we can easily test for non-diagonal
stuff by multiplying together the components of `$delta`

. This is how
`$is-hv`

is initialized.

The hash `%counts`

is populated in four different slots. The ones with
shorter names `1`

and `2`

count the passage of a segment over the
specific point, while the ones with longer names `over-1`

and `over-2`

keep track of those which see at least two segments intersect. This is
later used to figure out the puzzleâ€™s outputs.

At each loop, `$p1`

is advanced ahead at the end of the operations. This
remembers me so much of C.

Well, I think itâ€™s all for todayâ€¦ stay safe and have fun!

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