day_3_pt_2.pl

#!/usr/bin/perl
use warnings;
use strict;

#####
# Solution works for demo, but not for input
#####

our @inputs = get_inputs();

# Cache the first most common bit
my $first_mcb = find_mcb_in_position(0);

my $o2_gen_rate = find_o2_gen_rate($first_mcb, 1, \@inputs);
my $co2_scrub_rate = find_co2_scrub_rate($first_mcb ^ 0b1, 1, \@inputs);

# Print solution
# debug($o2_gen_rate);
# debug($co2_scrub_rate);

print $o2_gen_rate * $co2_scrub_rate;

sub find_o2_gen_rate
{
	my $query = $_[0];
	my $current_bit = $_[1];
	my @search_space = @{ $_[2] };

	if(scalar @search_space == 1){ return oct "0b".$search_space[0]; }
	elsif(scalar @search_space == 0){ die "Uh oh, you made a fucky wucky\n\tLast \$query: $query\n"; }

	my $mcb = find_mcb_in_position($current_bit, \@search_space);
	$query .= $mcb;

	@search_space = grep(/^$query/, @search_space);

	return find_o2_gen_rate($query, ++$current_bit, \@search_space);
}

sub find_co2_scrub_rate
{
	my $query = $_[0];
	my $current_bit = $_[1];
	my @search_space = @{ $_[2] };

	if(scalar @search_space == 1){ return oct "0b".$search_space[0]; }
	elsif(scalar @search_space == 0){ die "Uh oh, you made a fucky wucky\n\tLast \$query: $query\n"; }

	my $mcb = find_mcb_in_position($current_bit, \@search_space);
	$query .= $mcb ^ 0b1;

	@search_space = grep(/^$query/, @search_space);

	return find_co2_scrub_rate($query, ++$current_bit, \@search_space);
}



# Find the most common bit at a given index of an array of bytes
sub find_mcb_in_position
{
	my $index = $_[0];
	my @search_space;
	if(defined($_[1]))
	{
		@search_space = @{ $_[1] };
	}
	else
	{
		@search_space = @inputs;
	}

	my $word_length = length $search_space[0];
	
	my $low = 0;
	my $high = 0;
	foreach my $word (@search_space)
	{
		my $current_bit = substr($word, $index, 1);
		
		if($current_bit eq '0'){ $low++; }
		else{ $high++; }
	}

	return $high == $low ? clamp($high) : clamp($high - $low);
}

print "\n";

# Load the puzzle inputs into an array
# Loads the inputs from the file name supplied as first parameter
sub get_inputs
{
    if(!$ARGV[0])
    {
        die "Supply path to inputs";
    }

    my @lines;

    open(my $fh, '<', $ARGV[0]) or die "Failed to open file: $ARGV[0]";

    while(my $line = <$fh>)
    {
        chomp $line;
        push(@lines, $line);
    }

    return @lines;
}


# Return a value clamped between a minimum & a maximum
sub clamp
{
    my $value = $_[0];
    my $min = $_[1] || 0;
    my $max = $_[2] || 1;

    if($value < $min){ return $min; }
    if($value > $max){ return $max; }
    
    return $value;
}

1;