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#+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
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