31:[] 2f:{"title":"Advent of Code: 2021 Day 10","cells":[{"id":0,"value":"# Advent of Code: 2021 Day 10\n\nSee [Syntax Scoring](https://adventofcode.com/2021/day/10).","pinned":false,"hidden":false,"mode":"md"},{"id":1011,"value":"viewof inputChooser = Inputs.file({\n label: \"Puzzle input: \",\n accept: \".txt\",\n required: true\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":1009,"value":"## Part 1\n\nFind the first illegal character in each corrupted line of the navigation subsystem. **What is the total syntax error score for those errors?**","pinned":false,"hidden":false,"mode":"md"},{"id":126,"value":"### Parsing\n\nWe will store each line of input as an array of symbols.","pinned":false,"hidden":false,"mode":"md"},{"id":919,"value":"function parse(input) {\n return input.split(\"\\n\").map((s) => s.split(\"\"));\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":59,"value":"### Algorithm","pinned":false,"hidden":false,"mode":"md"},{"id":678,"value":"We push every opening symbol onto a stack. When we find a closing symbol we pop the last opening symbol off the stack and compare them. If they are not paired, we have a syntax error and can calculate the score.","pinned":false,"hidden":false,"mode":"md"},{"id":845,"value":"function errorScore(syms) {\n const stack = new Denque();\n for (const sym of syms) {\n if (sym == \"{\" || sym == \"(\" || sym == \"[\" || sym == \"<\") {\n stack.push(sym);\n } else {\n const lastOpen = stack.pop();\n if (sym == \")\" && lastOpen != \"(\") {\n return 3;\n }\n if (sym == \"]\" && lastOpen != \"[\") {\n return 57;\n }\n if (sym == \"}\" && lastOpen != \"{\") {\n return 1197;\n }\n if (sym == \">\" && lastOpen != \"<\") {\n return 25137;\n }\n }\n }\n return 0;\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":946,"value":"The answer is the sum of all error scores, with non-error lines scoring nothing.","pinned":false,"hidden":false,"mode":"md"},{"id":12,"value":"function part1(input) {\n return AOC.sum(parse(input).map((s) => errorScore(s)));\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":19,"value":"**${AOC.timer(part1,puzzleInput,10)}**","pinned":false,"hidden":false,"mode":"md"},{"id":797,"value":"AOC.assert(part1(puzzleInput), 392139)","pinned":false,"hidden":false,"mode":"ojs"},{"id":8,"value":"## Part 2\nFind the completion string for each incomplete line, score the completion strings, and sort the scores. **What is the middle score?**","pinned":false,"hidden":false,"mode":"md"},{"id":958,"value":"The symbols to complete will be the pairs of those remaining on the stack after processing each line. To calculate the score we don't need to convert the opening symbols on the stack to their paired closing symbol as we know that all lines are valid after filtering out the syntax errors.","pinned":false,"hidden":false,"mode":"md"},{"id":888,"value":"function autocompleteScore(syms) {\n const stack = new Denque();\n const score = (sym) => (sym == \"(\" ? 1 : sym == \"[\" ? 2 : sym == \"{\" ? 3 : 4);\n const accScore = (total, sym) => total * 5 + score(sym);\n\n for (const sym of syms) {\n sym == \"{\" || sym == \"(\" || sym == \"[\" || sym == \"<\"\n ? stack.push(sym)\n : stack.pop();\n }\n\n return stack.toArray().reverse().reduce(accScore, 0);\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":419,"value":"function part2(input) {\n const validLines = parse(input).filter((s) => errorScore(s) == 0);\n return AOC.median(validLines.map(autocompleteScore));\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":17,"value":"**${AOC.timer(part2,puzzleInput,10)}**","pinned":false,"hidden":false,"mode":"md"},{"id":800,"value":"AOC.assert(part2(puzzleInput), 4001832844)","pinned":false,"hidden":false,"mode":"ojs"},{"id":21,"value":"md `---`","pinned":false,"hidden":false,"mode":"ojs"},{"id":25,"value":"import { AOC, Denque } from \"@jwolondon/aoc-utilities\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":22,"value":"## Data","pinned":false,"hidden":false,"mode":"md"},{"id":28,"value":"test1 = `[({(<(())[]>[[{[]{<()<>>\n[(()[<>])]({[<{<<[]>>(\n{([(<{}[<>[]}>{[]{[(<()>\n(((({<>}<{<{<>}{[]{[]{}\n[[<[([]))<([[{}[[()]]]\n[{[{({}]{}}([{[{{{}}([]\n{<[[]]>}<{[{[{[]{()[[[]\n[<(<(<(<{}))><([]([]()\n<{([([[(<>()){}]>(<<{{\n<{([{{}}[<[[[<>{}]]]>[]]`","pinned":false,"hidden":false,"mode":"ojs"},{"id":31,"value":"puzzleInput = inputChooser.text()","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W31","stdlib":"1","titling":"auto"}