88 lines
3.5 KiB
Plaintext
88 lines
3.5 KiB
Plaintext
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# Advent of Code
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--- Day 2: Password Philosophy ---
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Your flight departs in a few days from the coastal airport; the easiest way down to the
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coast from here is via toboggan.
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The shopkeeper at the North Pole Toboggan Rental Shop is having a bad day. "Something's
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wrong with our computers; we can't log in!" You ask if you can take a look.
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Their password database seems to be a little corrupted: some of the passwords wouldn't have
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been allowed by the Official Toboggan Corporate Policy that was in effect when they were
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chosen.
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To try to debug the problem, they have created a list (your puzzle input) of passwords
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(according to the corrupted database) and the corporate policy when that password was set.
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For example, suppose you have the following list:
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1-3 a: abcde
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1-3 b: cdefg
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2-9 c: ccccccccc
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Each line gives the password policy and then the password. The password policy indicates
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the lowest and highest number of times a given letter must appear for the password to be
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valid. For example, 1-3 a means that the password must contain a at least 1 time and at
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most 3 times.
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In the above example, 2 passwords are valid. The middle password, cdefg, is not; it
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contains no instances of b, but needs at least 1. The first and third passwords are valid:
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they contain one a or nine c, both within the limits of their respective policies.
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How many passwords are valid according to their policies?
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Your puzzle answer was 636.
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--- Part Two ---
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While it appears you validated the passwords correctly, they don't seem to be what the
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Official Toboggan Corporate Authentication System is expecting.
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The shopkeeper suddenly realizes that he just accidentally explained the password policy
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rules from his old job at the sled rental place down the street! The Official Toboggan
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Corporate Policy actually works a little differently.
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Each policy actually describes two positions in the password, where 1 means the first
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character, 2 means the second character, and so on. (Be careful; Toboggan Corporate
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Policies have no concept of "index zero"!) Exactly one of these positions must contain the
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given letter. Other occurrences of the letter are irrelevant for the purposes of policy
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enforcement.
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Given the same example list from above:
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• 1-3 a: abcde is valid: position 1 contains a and position 3 does not.
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• 1-3 b: cdefg is invalid: neither position 1 nor position 3 contains b.
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• 2-9 c: ccccccccc is invalid: both position 2 and position 9 contain c.
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How many passwords are valid according to the new interpretation of the policies?
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Your puzzle answer was 588.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try another puzzle.
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If you still want to see it, you can get your puzzle input.
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2020/about
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. https://adventofcode.com/2020/events
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. https://adventofcode.com/2020/settings
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. https://adventofcode.com/2020/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2020/support
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. https://adventofcode.com/2020
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. https://adventofcode.com/2020
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. https://adventofcode.com/2020/support
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. https://adventofcode.com/2020/sponsors
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. https://adventofcode.com/2020/leaderboard
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. https://adventofcode.com/2020/stats
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. https://adventofcode.com/2020/sponsors
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. https://en.wikipedia.org/wiki/Toboggan
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. https://adventofcode.com/2020
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. https://adventofcode.com/2020/day/2/input
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