Add solution for 2021 day 03

2021/README.md

@@ -1,29 +1,29 @@
 # [Advent of Code 2021](https://adventofcode.com/2021)
 
-| Solved | Day | Language |
+| Day | Part 1 | Part 2 | Language |
-| :----: | :-: | :------- |
+| :-: | :----: | :----: | :------- |
-|   ✓    | 01  | Ruby     |
+| 01  |   ✓    |   ✓    | Ruby     |
-|   ✓    | 02  | Ada      |
+| 02  |   ✓    |   ✓    | Ada      |
-|        | 03  |          |
+| 03  |   ✓    |   ✓    | Perl     |
-|        | 04  |          |
+| 04  |        |        |          |
-|        | 05  |          |
+| 05  |        |        |          |
-|        | 06  |          |
+| 06  |        |        |          |
-|        | 07  |          |
+| 07  |        |        |          |
-|        | 08  |          |
+| 08  |        |        |          |
-|        | 09  |          |
+| 09  |        |        |          |
-|        | 10  |          |
+| 10  |        |        |          |
-|        | 11  |          |
+| 11  |        |        |          |
-|        | 12  |          |
+| 12  |        |        |          |
-|        | 13  |          |
+| 13  |        |        |          |
-|        | 14  |          |
+| 14  |        |        |          |
-|        | 15  |          |
+| 15  |        |        |          |
-|        | 16  |          |
+| 16  |        |        |          |
-|        | 17  |          |
+| 17  |        |        |          |
-|        | 18  |          |
+| 18  |        |        |          |
-|        | 19  |          |
+| 19  |        |        |          |
-|        | 20  |          |
+| 20  |        |        |          |
-|        | 21  |          |
+| 21  |        |        |          |
-|        | 22  |          |
+| 22  |        |        |          |
-|        | 23  |          |
+| 23  |        |        |          |
-|        | 24  |          |
+| 24  |        |        |          |
-|        | 25  |          |
+| 25  |        |        |          |

2021/day-03/common.pm

@@ -0,0 +1,24 @@
+package common;
+
+use strict;
+
+sub read_file {
+    my $input_path = $_[0];
+
+    open(FH, "<", $input_path) or die $!;
+
+    my @lines;
+
+    while(<FH>) {
+        my $line = $_;
+        $line =~ s/\s+$//; # rtrim
+        my @chars = split('', $line);
+        push(@lines, \@chars);
+    }
+
+    close(FH);
+
+    return @lines;
+}
+
+1; # module needs to return a "true value", because reasons

2021/day-03/inputs/sample.txt

@@ -0,0 +1,12 @@
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010

2021/day-03/part_one.pl

@@ -0,0 +1,43 @@
+#!/usr/bin/env perl
+
+# use warnings;
+use strict;
+use lib "./";
+use common;
+use Data::Dumper;
+
+sub part_one {
+    my $numbers = $_[0];
+    my $count = @$numbers;
+    my $digits = @{$numbers->[0]};
+    my @ones = ((0) x $digits);
+
+    for (@$numbers) {
+        my @row = @$_;
+        for my $idx (0 .. $#row) {
+            @ones[$idx] += 1 if @row[$idx] == "1";
+        }
+    }
+
+    my @gamma_rate = ();
+    my @epsilon_rate = ();
+
+    for (@ones) {
+        my $zeroes = $count - $_;
+        if ($zeroes < $_) {
+            push(@gamma_rate, 1);
+            push(@epsilon_rate, 0);
+        } else {
+            push(@gamma_rate, 0);
+            push(@epsilon_rate, 1);
+        }
+    }
+    my $gamma_rate = oct("0b" . join("", @gamma_rate));
+    my $epsilon_rate = oct("0b" . join("", @epsilon_rate));
+
+    return $gamma_rate * $epsilon_rate;
+}
+
+my @numbers = common::read_file($ARGV[0]);
+my $result = part_one(\@numbers);
+print $result, "\n";

2021/day-03/part_two.pl

@@ -0,0 +1,66 @@
+#!/usr/bin/env perl
+
+# use warnings;
+use strict;
+use lib "./";
+use common;
+use Data::Dumper;
+
+sub tally_digit_column {
+    my $numbers = $_[0];
+    my $digit = $_[1];
+
+    my @ones;
+    my @zeroes;
+
+    for my $num (@$numbers) {
+        if ($num->[$digit] eq "1") {
+            push(@ones, $num);
+        } else {
+            push(@zeroes, $num);
+        }
+    }
+
+    return (\@ones, \@zeroes);
+}
+
+sub part_two {
+    my $numbers = $_[0];
+    my $digits = @{$numbers->[0]};
+
+    my $highest = $numbers;
+    my $lowest = $numbers;
+
+    for my $idx (0..$digits) {
+        if (scalar(@$highest) != 1) {
+            my @results = tally_digit_column($highest, $idx);
+            my $ones = @results[0];
+            my $zeroes = @results[1];
+            if (scalar(@$ones) >= scalar(@$zeroes)) {
+                $highest = $ones;
+            } else {
+                $highest = $zeroes;
+            }
+        }
+
+        if (scalar(@$lowest) != 1) {
+            my @results = tally_digit_column($lowest, $idx);
+            my $ones = @results[0];
+            my $zeroes = @results[1];
+            if (scalar(@$zeroes) <= scalar(@$ones)) {
+                $lowest = $zeroes;
+            } else {
+                $lowest = $ones;
+            }
+        }
+    }
+
+    my $oxygen_rating = oct("0b" . join("", @{$highest->[0]}));
+    my $scrubber_rating = oct("0b" . join("", @{$lowest->[0]}));
+
+    return $oxygen_rating * $scrubber_rating;
+}
+
+my @numbers = common::read_file($ARGV[0]);
+my $result = part_two(\@numbers);
+print $result, "\n";