# ETOOBUSY đźš€ minimal blogging for the impatient

# AoC 2021/3 - Aiming for reuse

**TL;DR**

On with Advent of Code puzzle 3 from 2021: aiming for reuse of code.

This dayâ€™s puzzle introduces another theme that we will encounter again
during this yearâ€™s installment: the *wall of text*. There must be some
trick that the fast people use to sift through all that text, but I
honestly donâ€™t know.

```
#!/usr/bin/env raku
use v6;
sub MAIN ($filename = $?FILE.subst(/\.raku$/, '.sample')) {
my $inputs = get-inputs($filename);
my ($part1, $part2) = solve($inputs);
my $highlight = "\e[1;97;45m";
my $reset = "\e[0m";
put "part1 $highlight$part1$reset";
put "part2 $highlight$part2$reset";
}
sub get-inputs ($filename) {
$filename.IO.basename.IO.linesÂ».comb(/<[0 1]>/)Â».Array;
} ## end sub get_inputs ($filename = undef)
sub solve ($inputs) {
return (part1($inputs), part2($inputs));
}
sub part1 ($inputs) {
my @benchmarks = $inputs.elems / 2 xx $inputs[0].elems;
my @sums = [Z+] @$inputs;
my $epsilon = ((@sums Z< @benchmarks)Â».Int).join('');
my $gamma = TR/01/10/ given $epsilon;
return $epsilon.parse-base(2) * $gamma.parse-base(2);
}
sub part2 ($inputs) {
my $result = 1;
TARGET:
for 0, 1 -> $t {
my @candidates = @$inputs;
for 0 .. @candidates[0].end -> $bit {
my @s; # array of arrays of arrays, top indexed by 0, 1
@s[$_[$bit]].push: $_ for @candidates;
@candidates = @(@s[0] <= @s[1] ?? @s[$t] !! @s[1 - $t]);
if (@candidates.elems == 1) {
$result *= @candidates[0].join('').parse-base(2);
next TARGET;
}
}
}
return $result;
}
```

The first part is about considering each bit from the inputs, in
isolation to the other bits. To figure out whether there are more 0 or 1
values, itâ€™s sufficient to sum them all and compare against the half of
their number. This explains the `@benchmarks`

.

Thereâ€™s a lot of showing off in this part 1, e.g. the hyper-application of the zipped version of the sum. A compact way to sum all the inputs bit by bit (assuming, as it is in this case, that all input sequences are stored as arrays of 0 and 1 values).

Calculating `$epsilon`

is easy by comparing each bit position with the
benchmark. Again, we leverage the Zip operator here, though not in its
hyper form.

Itâ€™s interesting to note that `$gamma`

is the bitwise complement of
`$epsilon`

, so this is how we calculate it.

Part 2 is a bit moreâ€¦ *convoluted* and I could not figure out how to
show-off a few tricks. So there we go, with traditionally nested `for`

loops as well as `if`

conditions etc. etc. At each stage going ahead, we
work on a different â€śverticalâ€ť slice like before, this time restricted
to the the â€śsurvivorsâ€ť in the previous pass.

Soâ€¦ this completes the 2021 edition of Advent of Code. Did you enjoy it? Complete it? Get crazy for it? Let me know!

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