1 files changed, 152 insertions, 0 deletions
diff --git a/2020/day-06/README.org b/2020/day-06/README.org
new file mode 100644
index 0000000..508800c
--- /dev/null
+++ b/2020/day-06/README.org
@@ -0,0 +1,152 @@
+#+SETUPFILE: ~/.emacs.d/org-templates/level-3.org
+#+HTML_LINK_UP: ../../index.html#2020
+#+OPTIONS: toc:1
+#+EXPORT_FILE_NAME: index
+#+TITLE: Day 06 - Custom Customs
+
+* Puzzle
+- This puzzle is taken from: https://adventofcode.com/2020/day/6
+
+As your flight approaches the regional airport where you'll switch to a
+much larger plane, customs declaration forms are distributed to the
+passengers.
+
+The form asks a series of 26 yes-or-no questions marked a through z. All
+you need to do is identify the questions for which anyone in your group
+answers "yes". Since your group is just you, this doesn't take very
+long.
+
+However, the person sitting next to you seems to be experiencing a
+language barrier and asks if you can help. For each of the people in
+their group, you write down the questions for which they answer "yes",
+one per line. For example:
+#+BEGIN_SRC
+abcx
+abcy
+abcz
+#+END_SRC
+
+
+In this group, there are 6 questions to which anyone answered "yes": a,
+b, c, x, y, and z. (Duplicate answers to the same question don't count
+extra; each question counts at most once.)
+
+Another group asks for your help, then another, and eventually you've
+collected answers from every group on the plane (your puzzle input).
+Each group's answers are separated by a blank line, and within each
+group, each person's answers are on a single line. For example:
+#+BEGIN_SRC
+abc
+
+a
+b
+c
+
+ab
+ac
+
+a
+a
+a
+a
+
+b
+#+END_SRC
+
+This list represents answers from five groups:
+
+- The first group contains one person who answered "yes" to 3 questions:
+  a, b, and c.
+- The second group contains three people; combined, they answered "yes"
+  to 3 questions: a, b, and c.
+- The third group contains two people; combined, they answered "yes" to
+  3 questions: a, b, and c.
+- The fourth group contains four people; combined, they answered "yes"
+  to only 1 question, a.
+- The last group contains one person who answered "yes" to only 1
+  question, b.
+
+In this example, the sum of these counts is =3 + 3 + 3 + 1 + 1 = 11=.
+
+For each group, count the number of questions to which anyone answered
+"yes". What is the sum of those counts?
+** Part 2
+As you finish the last group's customs declaration, you notice that you
+misread one word in the instructions:
+
+You don't need to identify the questions to which anyone answered "yes";
+you need to identify the questions to which everyone answered "yes"!
+
+Using the same example as above:
+#+BEGIN_SRC
+abc
+
+a
+b
+c
+
+ab
+ac
+
+a
+a
+a
+a
+
+b
+#+END_SRC
+
+This list represents answers from five groups:
+
+- In the first group, everyone (all 1 person) answered "yes" to 3
+  questions: a, b, and c.
+- In the second group, there is no question to which everyone answered
+  "yes".
+- In the third group, everyone answered yes to only 1 question, a. Since
+  some people did not answer "yes" to b or c, they don't count.
+- In the fourth group, everyone answered yes to only 1 question, a.
+- In the fifth group, everyone (all 1 person) answered "yes" to 1
+  question, b.
+
+In this example, the sum of these counts is =3 + 0 + 1 + 1 + 1 = 6=.
+
+For each group, count the number of questions to which everyone answered
+"yes". What is the sum of those counts?
+* Solution
+The answers are stored in =@answers= & =$count= is kept for keeping the sum
+of counts.
+
+=%yes= is a hash that'll store the number of times each answer was marked
+"yes". =@individual_answers= holds each individual's answer from that
+group.
+#+BEGIN_SRC raku
+my $input = slurp "input";
+my @answers = $input.chomp.split("\n\n");
+my $count = 0;
+
+for @answers -> $answer {
+    my %yes;
+    my @individual_answers = $answer.split("\n");
+    %yes{$_} += 1 for @individual_answers.join.comb;
+
+    if $part == 1 {
+        ...
+    } elsif $part == 2 {
+        ...
+    }
+}
+say "Part $part: ", $count;
+#+END_SRC
+
+For part 1, we just set =$count= to number of keys in =%yes=.
+#+BEGIN_SRC raku
+$count += keys %yes;
+#+END_SRC
+** Part 2
+For part 2, iterate over keys of =%yes= & increment =$count= by 1 if that
+answer is marked yes by all individuals.
+#+BEGIN_SRC raku
+for keys %yes {
+    $count += 1 if %yes{$_} eq @individual_answers.elems;
+}
+#+END_SRC