88 lines
3.5 KiB
Plaintext
88 lines
3.5 KiB
Plaintext
# Advent of Code
|
||
|
||
--- 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 a look.
|
||
|
||
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 636.
|
||
|
||
--- Part Two ---
|
||
|
||
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 policies?
|
||
|
||
Your puzzle answer was 588.
|
||
|
||
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.
|
||
|
||
References
|
||
|
||
Visible links
|
||
. https://adventofcode.com/
|
||
. https://adventofcode.com/2020/about
|
||
. https://adventofcode.com/2020/events
|
||
. https://adventofcode.com/2020/settings
|
||
. https://adventofcode.com/2020/auth/logout
|
||
. Advent of Code Supporter
|
||
https://adventofcode.com/2020/support
|
||
. https://adventofcode.com/2020
|
||
. https://adventofcode.com/2020
|
||
. https://adventofcode.com/2020/support
|
||
. https://adventofcode.com/2020/sponsors
|
||
. https://adventofcode.com/2020/leaderboard
|
||
. https://adventofcode.com/2020/stats
|
||
. https://adventofcode.com/2020/sponsors
|
||
. https://en.wikipedia.org/wiki/Toboggan
|
||
. https://adventofcode.com/2020
|
||
. https://adventofcode.com/2020/day/2/input
|