34 lines
1.6 KiB
Markdown
34 lines
1.6 KiB
Markdown
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# 2019 Day 4: Secure Container
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Copyright (c) Eric Wastl
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#### [Direct Link](https://adventofcode.com/2019/day/4)
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## Part 1
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You arrive at the Venus fuel depot only to discover it's protected by a password. The Elves had written the password on a sticky note, but someone threw it out.
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However, they do remember a few key facts about the password:
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- It is a six-digit number.
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- The value is within the range given in your puzzle input.
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- Two adjacent digits are the same (like `22` in `122345`).
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- Going from left to right, the digits **never decrease**; they only ever increase or stay the same (like `111123` or `135679`).
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Other than the range rule, the following are true:
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- `111111` meets these criteria (double `11`, never decreases).
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- `223450` does not meet these criteria (decreasing pair of digits `50`).
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- `123789` does not meet these criteria (no double).
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**How many different passwords** within the range given in your puzzle input meet these criteria?
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## Part 2
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An Elf just remembered one more important detail: the two adjacent matching digits **are not part of a larger group of matching digits**.
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Given this additional criterion, but still ignoring the range rule, the following are now true:
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- `112233` meets these criteria because the digits never decrease and all repeated digits are exactly two digits long.
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- `123444` no longer meets the criteria (the repeated `44` is part of a larger group of `444`).
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- `111122` meets the criteria (even though `1` is repeated more than twice, it still contains a double `22`).
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**How many different passwords** within the range given in your puzzle input meet all of the criteria?
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