From feb34fac48dac79881bff93a2e60e69a08e432a2 Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Fri, 3 Dec 2021 10:29:58 -0500
Subject: Solve day 3 part 2

---
 2021/day03.pl | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

(limited to '2021/day03.pl')

diff --git a/2021/day03.pl b/2021/day03.pl
index 8a62021..7e8d2fc 100644
--- a/2021/day03.pl
+++ b/2021/day03.pl
@@ -1,17 +1,37 @@
 use strict;
 use warnings;
-my @nums;
+my ($bits, @nums);
 while (<>) {
 	chomp;
+	$bits = length($_);
 	push @nums, oct("0b".$_);
 }
-my $gamma = 0;
-for (my $i = 0; $i < 12; $i++) {
+sub countOnes {
+	my $i = shift;
 	my $ones = 0;
-	foreach (@nums) {
+	foreach (@_) {
 		$ones++ if $_ & (1 << $i);
 	}
-	$gamma |= 1 << $i if $ones > @nums / 2;
+	$ones;
+}
+my $gamma = 0;
+for (my $i = 0; $i < $bits; $i++) {
+	$gamma |= 1 << $i if countOnes($i, @nums) > @nums / 2;
 }
-my $epsilon = ~$gamma & 0xFFF;
+my $epsilon = ~$gamma & ((1 << $bits) - 1);
 print $gamma * $epsilon, "\n";
+my @o2 = @nums;
+my $i = $bits - 1;
+while (@o2 > 1) {
+	my $most = (countOnes($i, @o2) >= @o2 / 2) << $i;
+	@o2 = grep { ($_ & (1 << $i)) == $most } @o2;
+	$i--;
+}
+my @co2 = @nums;
+$i = $bits - 1;
+while (@co2 > 1) {
+	my $least = !(countOnes($i, @co2) >= @co2 / 2) << $i;
+	@co2 = grep { ($_ & (1 << $i)) == $least } @co2;
+	$i--;
+}
+print $o2[0] * $co2[0], "\n";
-- 
cgit 1.4.1

216a65a&amp;follow=1'>diff</a> <a href='https://adventofcode.com'>homepage</a></td><td class='form'><form class='right' method='get' action='/aoc/log/2016'>
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<div class='path'>path: <a href='/aoc/log/?id=ee407104c9723b365ce65702a5f29e957216a65a&amp;showmsg=1&amp;follow=1'>root</a>/<a href='/aoc/log/2016?id=ee407104c9723b365ce65702a5f29e957216a65a&amp;showmsg=1&amp;follow=1'>2016</a> (<a href='/aoc/log/2016?id=ee407104c9723b365ce65702a5f29e957216a65a&amp;showmsg=1'>unfollow</a>)</div><div class='content'><table class='list nowrap'><tr class='nohover'><th></th><th class='left'>Commit message (<a href='/aoc/log/2016?id=ee407104c9723b365ce65702a5f29e957216a65a&amp;follow=1'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2020-11-22 00:14:25 -0500'>2020-11-22</span></td><td class='logsubject'><a href='/aoc/commit/2017/src/bin/day01.rs?id=c6f3bfe8f68d2e71d10d422df281682cfba60415&amp;follow=1'>Day 1, part 2</a></td><td>June McEnroe</td></tr>
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</td></tr>
<tr class='logheader'><td><span title='2020-11-22 00:14:25 -0500'>2020-11-22</span></td><td class='logsubject'><a href='/aoc/commit/2017/src/bin/day01.rs?id=e37a5af3a9de37537025b11bd9fd54487459edff&amp;follow=1'>Day 1</a></td><td>June McEnroe</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
</td></tr>
<tr class='logheader'><td><span title='2020-11-22 00:14:25 -0500'>2020-11-22</span></td><td class='logsubject'><a href='/aoc/commit/2016/src/bin/day25.rs?id=051be932a389b8bc3ea5d4626575454844639066&amp;follow=1'>Move to 2016 directory</a></td><td>June McEnroe