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. * , 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, 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). * {,,,}, 1 group. * {{},{},{},{}}, 5 groups. * {{},{},{},{}}, 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. * {,,,}, score of 1. * {{},{},{},{}}, score of 1 + 2 + 2 + 2 + 2 = 9. * {{},{},{},{}}, score of 1 + 2 + 2 + 2 + 2 = 9. * {{},{},{},{}}, score of 1 + 2 = 3. What is the total score for all groups in your input? Your puzzle answer was ______. --- 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. * , 17 characters. * <<<<>, 3 characters. * <{!>}>, 2 characters. * , 0 characters. * >, 0 characters. * <{o"i!a,<{i, 10 characters. How many non-canceled characters are within the garbage in your puzzle input? Your puzzle answer was ______. 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. References Visible links . http://adventofcode.com/ . http://adventofcode.com/2017/about . http://adventofcode.com/2017/support . http://adventofcode.com/2017/events . http://adventofcode.com/2017/settings . http://adventofcode.com/2017/auth/logout . http://adventofcode.com/2017 . http://adventofcode.com/2017 . http://adventofcode.com/2017/leaderboard . http://adventofcode.com/2017/stats . http://adventofcode.com/2017/sponsors . http://adventofcode.com/2017/sponsors . http://adventofcode.com/2017 . http://adventofcode.com/2017/day/9/input