AdventOfCode/2015/11/11.md

## \-\-- Day 11: Corporate Policy \-\--

Santa\'s previous password expired, and he needs help choosing a new
one.

To help him remember his new password after the old one expires, Santa
has devised a method of coming up with a password based on the previous
one. Corporate policy dictates that passwords must be exactly eight
lowercase letters (for security reasons), so he finds his new password
by *incrementing* his old password string repeatedly until it is valid.

Incrementing is just like counting with numbers: `xx`, `xy`, `xz`, `ya`,
`yb`, and so on. Increase the rightmost letter one step; if it was `z`,
it wraps around to `a`, and repeat with the next letter to the left
until one doesn\'t wrap around.

Unfortunately for Santa, a new Security-Elf recently started, and he has
imposed some additional password requirements:

-   Passwords must include one increasing straight of at least three
    letters, like `abc`, `bcd`, `cde`, and so on, up to `xyz`. They
    cannot skip letters; `abd` doesn\'t count.
-   Passwords may not contain the letters `i`, `o`, or `l`, as these
    letters can be mistaken for other characters and are therefore
    confusing.
-   Passwords must contain at least two different, non-overlapping pairs
    of letters, like `aa`, `bb`, or `zz`.

For example:

-   `hijklmmn` meets the first requirement (because it contains the
    straight `hij`) but fails the second requirement requirement
    (because it contains `i` and `l`).
-   `abbceffg` meets the third requirement (because it repeats `bb` and
    `ff`) but fails the first requirement.
-   `abbcegjk` fails the third requirement, because it only has one
    double letter (`bb`).
-   The next password after `abcdefgh` is `abcdffaa`.
-   The next password after `ghijklmn` is `ghjaabcc`, because you
    eventually skip all the passwords that start with `ghi...`, since
    `i` is not allowed.

Given Santa\'s current password (your puzzle input), what should his
*next password* be?

Your puzzle answer was `hxbxxyzz`.

## \-\-- Part Two \-\-- {#part2}

Santa\'s password [expired
again]{title="The corporate policy says your password expires after 12 seconds.  For security."}.
What\'s the next one?

Your puzzle answer was `hxcaabcc`.

Both parts of this puzzle are complete! They provide two gold stars:
\*\*

At this point, you should [return to your Advent calendar](/2015) and
try another puzzle.

Your puzzle input was `hxbxwxba`{.puzzle-input}.