2021/day03.pl


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use strict;
use warnings;
my ($bits, @nums);
while (<>) {
	chomp;
	$bits = length($_);
	push @nums, oct("0b".$_);
}
sub countOnes {
	my $i = shift;
	my $ones = 0;
	foreach (@_) {
		$ones++ if $_ & (1 << $i);
	}
	$ones;
}
my $gamma = 0;
for (my $i = 0; $i < $bits; $i++) {
	$gamma |= 1 << $i if countOnes($i, @nums) > @nums / 2;
}
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";