This is a solution to Advent of Code 2023 day 9, written in Raku.
https://adventofcode.com/2023/day/9
Part One
The amphipod would like to move file blocks one at a time from the end of the disk to the leftmost free space block (until there are no gaps remaining between file blocks).
Compact the amphipod's hard drive using the process he requested. What is the resulting filesystem checksum?
use Test;
sub day-nine($file, :$debug = False) {
my @digits = $file.IO.slurp.chomp.comb;
my $id = 0;
my $is-file = True;
my @disk = @digits.map(
-> $d {
LEAVE $is-file = !$is-file;
if $is-file {
LEAVE $id += 1;
$id xx $d
} else {
'.' xx $d
}
}
).flat;
say @disk.join if $debug;
for 0..* -> $i {
@disk.pop while @disk[*-1] eq '.';
last if $i >= +@disk;
if @disk[$i] eq '.' {
@disk[$i] = @disk.pop;
}
}
say @disk.join if $debug;
[+] @disk.kv.map(-> $k, $v { $k * $v });
}
say day-nine('test-9.txt', :debug);
is day-nine('test-9.txt'), 1928, 'example input';
say day-nine('input-9.txt');00...111...2...333.44.5555.6666.777.888899 0099811188827773336446555566 1928 ok 1 - example input 6415184586041
Part Two
The eager amphipod already has a new plan: rather than move individual blocks, he'd like to try compacting the files on his disk by moving whole files instead…
Start over, now compacting the amphipod's hard drive using this new method instead. What is the resulting filesystem checksum?
use Test;
sub day-nine($file, :$debug = False) {
my @digits = $file.IO.slurp.chomp.comb;
my $id = 0;
my $is-file = True;
my %file-spans;
my @free-spans;
my $pos = 0;
my @disk = @digits.map(
-> $d {
LEAVE $is-file = !$is-file;
LEAVE $pos += $d;
if $is-file {
LEAVE $id += 1;
%file-spans{$id} = $pos..^$pos+$d;
$id xx $d
} else {
@free-spans.push: $pos..^$pos+$d;
'.' xx $d
}
}
).flat;
say @disk.join if $debug;
for $id ^... 0 -> $n {
for ^+@free-spans -> $i {
my $span = @free-spans[$i];
my $file = %file-spans{$n};
last if $file.min < $span.min;
if +$file <= +$span {
my $pos = $span.min;
$file.list.map(
-> $f {
@disk[$pos] = @disk[$f];
@disk[$f] = '.';
$pos += 1;
});
@free-spans[$i] = $pos ..^ $span.max;
last;
}
}
}
say @disk.join if $debug;
[+] @disk.kv.map(-> $k, $v { $k * $v if $v ne '.' });
}
say day-nine('test-9.txt', :debug);
is day-nine('test-9.txt'), 2858, 'example input';
say day-nine('input-9.txt');
say "Took " ~ (now - ENTER now).base(10, 2) ~ "s";00...111...2...333.44.5555.6666.777.888899 00992111777.44.333....5555.6666.....8888.. 2858 ok 1 - example input 6436819084274 Took 25.67s