aoc2021

commit 64765fdf766b36b62669f840d6aa2864039c5d61
parent 750d7c759650bbd6cd4deae54089c87149705de4
Author: Samir Parikh <noreply@samirparikh.com>
Date:   Fri,  3 Dec 2021 15:38:01 +0000

Merge branch 'dev'

Diffstat:
A
day03.pl
 | 
52
++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 52 insertions(+), 0 deletions(-)
diff --git a/day03.pl b/day03.pl
@@ -0,0 +1,52 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use v5.22;
+#use Data::Dumper;
+
+if (@ARGV !=1) {
+    die "Usage: $0 [input-filename]";
+}
+
+my $input_filename = $ARGV[0];
+open my $filehandle, '<', $input_filename or
+    die "Could not open input file $input_filename: $!";
+
+chomp( my @input = ( <$filehandle> ) );
+
+# Part 1
+my $len = length($input[0]) - 1; # number of bits - 1
+my %count_0 = ();
+my %count_1 = ();
+my $gamma_rate = "";
+my $epsilon_rate = "";
+
+foreach (@input) {
+    my @diagnostic = split //;
+    for (0 .. $len) {
+        if ($diagnostic[$_]) { # bit at position $_ is 1
+            $count_1{$_}++;
+        } else {
+            $count_0{$_}++;
+        }
+    }
+}
+
+for (0 .. $len) { # find which bit occurs the most at each position
+    if ($count_0{$_} > $count_1{$_}) {
+        $gamma_rate .= "0";
+        $epsilon_rate .= "1";
+    } else {
+        $gamma_rate .= "1";
+        $epsilon_rate .= "0";
+    }
+}
+
+# From the perlfunc man page:
+#        oct EXPR
+#        oct Interprets EXPR as an octal string and returns the corresponding
+#            value.  (If EXPR happens to start off with "0x", interprets it as a
+#            hex string.  If EXPR starts off with "0b", it is interpreted as a
+#            binary string.  Leading whitespace is ignored in all three cases.)
+say oct("0b" . $gamma_rate) * oct("0b" . $epsilon_rate);