2021 Day 10 Complete
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# Advent of Code
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--- Day 10: Syntax Scoring ---
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You ask the submarine to determine the best route out of the deep-sea cave, but it only replies:
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Syntax error in navigation subsystem on line: all of them
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All of them?! The damage is worse than you thought. You bring up a copy of the navigation subsystem (your puzzle input).
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The navigation subsystem syntax is made of several lines containing chunks. There are one or more chunks on each line, and chunks contain zero or more other
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chunks. Adjacent chunks are not separated by any delimiter; if one chunk stops, the next chunk (if any) can immediately start. Every chunk must open and close
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with one of four legal pairs of matching characters:
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• If a chunk opens with (, it must close with ).
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• If a chunk opens with [, it must close with ].
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• If a chunk opens with {, it must close with }.
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• If a chunk opens with <, it must close with >.
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So, () is a legal chunk that contains no other chunks, as is []. More complex but valid chunks include ([]), {()()()}, <([{}])>, [<>({}){}[([])<>]], and even
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(((((((((()))))))))).
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Some lines are incomplete, but others are corrupted. Find and discard the corrupted lines first.
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A corrupted line is one where a chunk closes with the wrong character - that is, where the characters it opens and closes with do not form one of the four
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legal pairs listed above.
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Examples of corrupted chunks include (], {()()()>, (((()))}, and <([]){()}[{}]). Such a chunk can appear anywhere within a line, and its presence causes the
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whole line to be considered corrupted.
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For example, consider the following navigation subsystem:
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[({(<(())[]>[[{[]{<()<>>
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[(()[<>])]({[<{<<[]>>(
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{([(<{}[<>[]}>{[]{[(<()>
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(((({<>}<{<{<>}{[]{[]{}
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[[<[([]))<([[{}[[()]]]
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[{[{({}]{}}([{[{{{}}([]
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{<[[]]>}<{[{[{[]{()[[[]
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[<(<(<(<{}))><([]([]()
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<{([([[(<>()){}]>(<<{{
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<{([{{}}[<[[[<>{}]]]>[]]
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Some of the lines aren't corrupted, just incomplete; you can ignore these lines for now. The remaining five lines are corrupted:
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• {([(<{}[<>[]}>{[]{[(<()> - Expected ], but found } instead.
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• [[<[([]))<([[{}[[()]]] - Expected ], but found ) instead.
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• [{[{({}]{}}([{[{{{}}([] - Expected ), but found ] instead.
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• [<(<(<(<{}))><([]([]() - Expected >, but found ) instead.
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• <{([([[(<>()){}]>(<<{{ - Expected ], but found > instead.
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Stop at the first incorrect closing character on each corrupted line.
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Did you know that syntax checkers actually have contests to see who can get the high score for syntax errors in a file? It's true! To calculate the syntax
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error score for a line, take the first illegal character on the line and look it up in the following table:
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• ): 3 points.
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• ]: 57 points.
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• }: 1197 points.
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• >: 25137 points.
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In the above example, an illegal ) was found twice (2*3 = 6 points), an illegal ] was found once (57 points), an illegal } was found once (1197 points), and an
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illegal > was found once (25137 points). So, the total syntax error score for this file is 6+57+1197+25137 = 26397 points!
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Find the first illegal character in each corrupted line of the navigation subsystem. What is the total syntax error score for those errors?
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Your puzzle answer was 296535.
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--- Part Two ---
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Now, discard the corrupted lines. The remaining lines are incomplete.
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Incomplete lines don't have any incorrect characters - instead, they're missing some closing characters at the end of the line. To repair the navigation
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subsystem, you just need to figure out the sequence of closing characters that complete all open chunks in the line.
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You can only use closing characters (), ], }, or >), and you must add them in the correct order so that only legal pairs are formed and all chunks end up
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closed.
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In the example above, there are five incomplete lines:
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• [({(<(())[]>[[{[]{<()<>> - Complete by adding }}]])})].
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• [(()[<>])]({[<{<<[]>>( - Complete by adding )}>]}).
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• (((({<>}<{<{<>}{[]{[]{} - Complete by adding }}>}>)))).
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• {<[[]]>}<{[{[{[]{()[[[] - Complete by adding ]]}}]}]}>.
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• <{([{{}}[<[[[<>{}]]]>[]] - Complete by adding ])}>.
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Did you know that autocomplete tools also have contests? It's true! The score is determined by considering the completion string character-by-character. Start
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with a total score of 0. Then, for each character, multiply the total score by 5 and then increase the total score by the point value given for the character
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in the following table:
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• ): 1 point.
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• ]: 2 points.
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• }: 3 points.
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• >: 4 points.
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So, the last completion string above - ])}> - would be scored as follows:
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• Start with a total score of 0.
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• Multiply the total score by 5 to get 0, then add the value of ] (2) to get a new total score of 2.
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• Multiply the total score by 5 to get 10, then add the value of ) (1) to get a new total score of 11.
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• Multiply the total score by 5 to get 55, then add the value of } (3) to get a new total score of 58.
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• Multiply the total score by 5 to get 290, then add the value of > (4) to get a new total score of 294.
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The five lines' completion strings have total scores as follows:
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• }}]])})] - 288957 total points.
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• )}>]}) - 5566 total points.
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• }}>}>)))) - 1480781 total points.
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• ]]}}]}]}> - 995444 total points.
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• ])}> - 294 total points.
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Autocomplete tools are an odd bunch: the winner is found by sorting all of the scores and then taking the middle score. (There will always be an odd number of
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scores to consider.) In this example, the middle score is 288957 because there are the same number of scores smaller and larger than it.
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Find the completion string for each incomplete line, score the completion strings, and sort the scores. What is the middle score?
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Your puzzle answer was 4245130838.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try another puzzle.
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If you still want to see it, you can get your puzzle input.
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2021/about
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. https://adventofcode.com/2021/events
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. https://adventofcode.com/2021/settings
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. https://adventofcode.com/2021/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2021/support
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. https://adventofcode.com/2021
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. https://adventofcode.com/2021
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. https://adventofcode.com/2021/support
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. https://adventofcode.com/2021/sponsors
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. https://adventofcode.com/2021/leaderboard
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. https://adventofcode.com/2021/stats
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. https://adventofcode.com/2021/sponsors
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. https://adventofcode.com/2021
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. https://adventofcode.com/2021/day/10/input
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