Advent of Code

--- Day 9: Stream Processing ---

   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 >.

   Here are some examples of whole streams and the number of groups they contain:

     * {}, 1 group.
     * {{{}}}, 3 groups.
     * {{},{}}, also 3 groups.
     * {{{},{},{{}}}}, 6 groups.
     * {<{},{},{{}}>}, 1 group (which itself contains garbage).
     * {<a>,<a>,<a>,<a>}, 1 group.
     * {{<a>},{<a>},{<a>},{<a>}}, 5 groups.
     * {{<!>},{<!>},{<!>},{<a>}}, 2 groups (since all but the last > are canceled).

   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.)

     * {}, score of 1.
     * {{{}}}, score of 1 + 2 + 3 = 6.
     * {{},{}}, score of 1 + 2 + 2 = 5.
     * {{{},{},{{}}}}, score of 1 + 2 + 3 + 3 + 3 + 4 = 16.
     * {<a>,<a>,<a>,<a>}, score of 1.
     * {{<ab>},{<ab>},{<ab>},{<ab>}}, score of 1 + 2 + 2 + 2 + 2 = 9.
     * {{<!!>},{<!!>},{<!!>},{<!!>}}, score of 1 + 2 + 2 + 2 + 2 = 9.
     * {{<a!>},{<a!>},{<a!>},{<ab>}}, score of 1 + 2 = 3.

   What is the total score for all groups in your input?

   Your puzzle answer was 10820.

--- 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 < and > don't count, nor do any canceled
   characters or the ! doing the canceling.

     * <>, 0 characters.
     * <random characters>, 17 characters.
     * <<<<>, 3 characters.
     * <{!>}>, 2 characters.
     * <!!>, 0 characters.
     * <!!!>>, 0 characters.
     * <{o"i!a,<{i<a>, 10 characters.

   How many non-canceled characters are within the garbage in your puzzle input?

   Your puzzle answer was 5547.

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

   At this point, you should return to your advent calendar and try another puzzle.

   If you still want to see it, you can get your puzzle input.

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