From c2219772863be4c5d66d88617c2a65b7ed0a4e76 Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Fri, 15 Dec 2023 20:28:53 -0500
Subject: Solve day 9 part 2
---
2023/day09.pl | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/2023/day09.pl b/2023/day09.pl
index 5ec28b2..c9814c9 100644
--- a/2023/day09.pl
+++ b/2023/day09.pl
@@ -13,16 +13,21 @@ sub extrapolate {
while (any { $_ != 0 } @{$diffs[0]}) {
unshift @diffs, [diff(@{$diffs[0]})];
}
+ unshift @{$diffs[0]}, 0;
push @{$diffs[0]}, 0;
for (1 .. $#diffs) {
- push @{$diffs[$_]}, $diffs[$_-1]->[-1] + $diffs[$_]->[-1];
+ unshift @{$diffs[$_]}, $diffs[$_][0] - $diffs[$_-1][0];
+ push @{$diffs[$_]}, $diffs[$_-1][-1] + $diffs[$_][-1];
}
- $diffs[-1]->[-1];
+ ($diffs[-1][0], $diffs[-1][-1]);
}
-my $sum = 0;
+my ($sum, $sum2) = (0, 0);
while (<>) {
chomp;
my @history = split(/ /);
- $sum += extrapolate(@history);
+ my ($first, $last) = extrapolate(@history);
+ $sum += $last;
+ $sum2 += $first;
}
print $sum, "\n";
+print $sum2, "\n";
--
cgit 1.4.1