62 lines
3.3 KiB
Plaintext
62 lines
3.3 KiB
Plaintext
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--- Day 9: Stream Processing ---
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A large stream blocks your path. According to the locals, it's not safe to cross the stream at the moment because it's full of garbage. You look down at the stream; rather than water, you discover that it's a stream of characters.
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You sit for a while and record part of the stream (your puzzle input). The characters represent groups - sequences that begin with { and end with }. Within a group, there are zero or more other things, separated by commas: either another group or garbage. Since groups can contain other groups, a } only closes the most-recently-opened unclosed group - that is, they are nestable. Your puzzle input represents a single, large group which itself contains many smaller ones.
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Sometimes, instead of a group, you will find garbage. Garbage begins with < and ends with >. Between those angle brackets, almost any character can appear, including { and }. Within garbage, < has no special meaning.
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In a futile attempt to clean up the garbage, some program has canceled some of the characters within it using !: inside garbage, any character that comes after ! should be ignored, including <, >, and even another !.
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You don't see any characters that deviate from these rules. Outside garbage, you only find well-formed groups, and garbage always terminates according to the rules above.
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Here are some self-contained pieces of garbage:
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<>, empty garbage.
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<random characters>, garbage containing random characters.
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<<<<>, because the extra < are ignored.
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<{!>}>, because the first > is canceled.
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<!!>, because the second ! is canceled, allowing the > to terminate the garbage.
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<!!!>>, because the second ! and the first > are canceled.
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<{o"i!a,<{i<a>, which ends at the first >.
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Here are some examples of whole streams and the number of groups they contain:
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{}, 1 group.
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{{{}}}, 3 groups.
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{{},{}}, also 3 groups.
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{{{},{},{{}}}}, 6 groups.
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{<{},{},{{}}>}, 1 group (which itself contains garbage).
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{<a>,<a>,<a>,<a>}, 1 group.
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{{<a>},{<a>},{<a>},{<a>}}, 5 groups.
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{{<!>},{<!>},{<!>},{<a>}}, 2 groups (since all but the last > are canceled).
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Your goal is to find the total score for all groups in your input. Each group is assigned a score which is one more than the score of the group that immediately contains it. (The outermost group gets a score of 1.)
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{}, score of 1.
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{{{}}}, score of 1 + 2 + 3 = 6.
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{{},{}}, score of 1 + 2 + 2 = 5.
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{{{},{},{{}}}}, score of 1 + 2 + 3 + 3 + 3 + 4 = 16.
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{<a>,<a>,<a>,<a>}, score of 1.
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{{<ab>},{<ab>},{<ab>},{<ab>}}, score of 1 + 2 + 2 + 2 + 2 = 9.
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{{<!!>},{<!!>},{<!!>},{<!!>}}, score of 1 + 2 + 2 + 2 + 2 = 9.
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{{<a!>},{<a!>},{<a!>},{<ab>}}, score of 1 + 2 = 3.
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What is the total score for all groups in your input?
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--- Part Two ---
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Now, you're ready to remove the garbage.
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To prove you've removed it, you need to count all of the characters within the garbage. The leading and trailing < and > don't count, nor do any canceled characters or the ! doing the canceling.
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<>, 0 characters.
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<random characters>, 17 characters.
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<<<<>, 3 characters.
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<{!>}>, 2 characters.
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<!!>, 0 characters.
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<!!!>>, 0 characters.
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<{o"i!a,<{i<a>, 10 characters.
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How many non-canceled characters are within the garbage in your puzzle input?
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