day09: Day 09: Stream Processing
In tjmahr/adventofcode17: Advent of Code 2017

Description Usage Arguments Details Examples

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process_stream(stream)

count_garbage(stream)

stream

a string to process

Part One

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.

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.

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.

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 !.

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.

Here are some self-contained pieces of garbage:

<>, empty garbage.
<random characters>, garbage containing random characters.
<<<<>, because the extra < are ignored.
<{!>}>, because the first > is canceled.
<!!>, because the second ! is canceled, allowing the > to terminate the garbage.
<!!!>>, because the second ! and the first > are canceled.
<o"i!a,<\{i<a>}, which ends at the first \code{>}. } Here are some examples of whole streams and the number of groups they contain: \itemize{ \item \code{\{\}}, \code{1} group. \item \code{\{\{\{\}\}\}}, \code{3} groups. \item \code{\{\{\},\{\}\}}, also \code{3} groups. \item \code{\{\{\{\},\{\},\{\{\}\}\}\}}, \code{6} groups. \item \code{\{<\{\},\{\},\{\{\}\}>\}}, \code{1} group (which itself contains garbage). \item \code{\{<a>,<a>,<a>,<a>\}}, \code{1} group. \item \code{\{\{<a>\},\{<a>\},\{<a>\},\{<a>\}\}}, \code{5} groups. \item \code{\{\{<!>\},\{<!>\},\{<!>\},\{<a>\}\}}, \code{2} groups (since all but the last \code{>} are canceled). } Your goal is to find the total score for all groups in your input. Each group is assigned a \emph{score} which is one more than the score of the group that immediately contains it. (The outermost group gets a score of \code{1}.) \itemize{ \item \code{\{\}}, score of \code{1}. \item \code{\{\{\{\}\}\}}, score of \code{1 + 2 + 3 = 6}. \item \code{\{\{\},\{\}\}}, score of \code{1 + 2 + 2 = 5}. \item \code{\{\{\{\},\{\},\{\{\}\}\}\}}, score of \code{1 + 2 + 3 + 3 + 3 + 4 = 16}. \item \code{\{<a>,<a>,<a>,<a>\}}, score of \code{1}. \item \code{\{\{<ab>\},\{<ab>\},\{<ab>\},\{<ab>\}\}}, score of \code{1 + 2 + 2 + 2 + 2 = 9}. \item \code{\{\{<!!>\},\{<!!>\},\{<!!>\},\{<!!>\}\}}, score of \code{1 + 2 + 2 + 2 + 2 = 9}. \item \code{\{\{<a!>\},\{<a!>\},\{<a!>\},\{<ab>\}\}}, score of \code{1 + 2 = 3}. } \emph{What is the total score} for all groups in your input? \strong{Part Two} Now, you're ready to remove the garbage. To prove you've removed it, you need to count all of the characters within the garbage. The leading and trailing \code{<} and \code{>} don't count, nor do any canceled characters or the \code{!} doing the canceling. \itemize{ \item \code{<>}, \code{0} characters. \item \code{<random characters>}, \code{17} characters. \item \code{<<<<>}, \code{3} characters. \item \code{<\{!>\}>}, \code{2} characters. \item \code{<!!>}, \code{0} characters. \item \code{<!!!>>}, \code{0} characters. \item \code{<\{o"i!a,<{i<a>, 10 characters.