50 lines
2.0 KiB
Markdown
50 lines
2.0 KiB
Markdown
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## \-\-- Day 11: Corporate Policy \-\--
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Santa\'s previous password expired, and he needs help choosing a new
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one.
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To help him remember his new password after the old one expires, Santa
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has devised a method of coming up with a password based on the previous
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one. Corporate policy dictates that passwords must be exactly eight
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lowercase letters (for security reasons), so he finds his new password
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by *incrementing* his old password string repeatedly until it is valid.
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Incrementing is just like counting with numbers: `xx`, `xy`, `xz`, `ya`,
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`yb`, and so on. Increase the rightmost letter one step; if it was `z`,
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it wraps around to `a`, and repeat with the next letter to the left
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until one doesn\'t wrap around.
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Unfortunately for Santa, a new Security-Elf recently started, and he has
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imposed some additional password requirements:
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- Passwords must include one increasing straight of at least three
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letters, like `abc`, `bcd`, `cde`, and so on, up to `xyz`. They
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cannot skip letters; `abd` doesn\'t count.
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- Passwords may not contain the letters `i`, `o`, or `l`, as these
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letters can be mistaken for other characters and are therefore
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confusing.
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- Passwords must contain at least two different, non-overlapping pairs
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of letters, like `aa`, `bb`, or `zz`.
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For example:
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- `hijklmmn` meets the first requirement (because it contains the
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straight `hij`) but fails the second requirement requirement
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(because it contains `i` and `l`).
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- `abbceffg` meets the third requirement (because it repeats `bb` and
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`ff`) but fails the first requirement.
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- `abbcegjk` fails the third requirement, because it only has one
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double letter (`bb`).
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- The next password after `abcdefgh` is `abcdffaa`.
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- The next password after `ghijklmn` is `ghjaabcc`, because you
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eventually skip all the passwords that start with `ghi...`, since
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`i` is not allowed.
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Given Santa\'s current password (your puzzle input), what should his
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*next password* be?
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Your puzzle input is `hxbxwxba`{.puzzle-input}.
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Answer:
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