|author||Bryan Brattlof <email@example.com>||2020-12-11 12:29:12 -0500|
|committer||Bryan Brattlof <firstname.lastname@example.org>||2020-12-11 12:29:26 -0500|
day02: add questions
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+Day 2: Password Philosophy
+Your flight departs in a few days from the coastal airport; the easiest way down
+to the coast from here is via toboggan.
+The shopkeeper at the North Pole Toboggan Rental Shop is having a bad day.
+"Something's wrong with our computers; we can't log in!" You ask if you can take
+Their password database seems to be a little corrupted: some of the passwords
+wouldn't have been allowed by the Official Toboggan Corporate Policy that was in
+effect when they were chosen.
+To try to debug the problem, they have created a list (your puzzle input) of
+passwords (according to the corrupted database) and the corporate policy when
+that password was set.
+For example, suppose you have the following list:
+ 1-3 a: abcde
+ 1-3 b: cdefg
+ 2-9 c: ccccccccc
+Each line gives the password policy and then the password. The password policy
+indicates the lowest and highest number of times a given letter must appear for
+the password to be valid. For example, 1-3 a means that the password must
+contain a at least 1 time and at most 3 times.
+In the above example, 2 passwords are valid. The middle password, cdefg, is not;
+it contains no instances of b, but needs at least 1. The first and third
+passwords are valid: they contain one a or nine c, both within the limits of
+their respective policies.
+How many passwords are valid according to their policies?
+Your puzzle answer was 422.
+While it appears you validated the passwords correctly, they don't seem to be
+what the Official Toboggan Corporate Authentication System is expecting.
+The shopkeeper suddenly realizes that he just accidentally explained the
+password policy rules from his old job at the sled rental place down the street!
+The Official Toboggan Corporate Policy actually works a little differently.
+Each policy actually describes two positions in the password, where 1 means the
+first character, 2 means the second character, and so on. (Be careful; Toboggan
+Corporate Policies have no concept of "index zero"!) Exactly one of these
+positions must contain the given letter. Other occurrences of the letter are
+irrelevant for the purposes of policy enforcement.
+Given the same example list from above:
+- '1-3 a: abcde' is valid: position 1 contains a and position 3 does not.
+- '1-3 b: cdefg' is invalid: neither position 1 nor position 3 contains b.
+- '2-9 c: ccccccccc' is invalid: both position 2 and position 9 contain c.
+How many passwords are valid according to the new interpretation of the
+Your puzzle answer was 451.
+Both parts of this puzzle are complete! They provide two gold stars: **
+At this point, you should return to your Advent calendar and try another puzzle.
+If you still want to see it, you can get your puzzle input.
+You can also [Share on Twitter Mastodon] this puzzle.