Are you participating in the Advent of code this year?
If you don't know what the advent of code is, it's a website where you'll find a daily challenge (every day it gets harder). It's a really fun event, you should participate!
I try to solve the exercises using either JavaScript or TypeScript and will share my solutions daily (with one day delay so no one can cheat!). I only share the solution for the second part.
Again a fun one where you have to generate a RegEx to validate some strings. Part one was super nice, I just had a function to generate the RegEx and... voilà. For part 2, I had to hardcode the two rules for 11 and 8, then merge then for the RegEx to work. Not beautiful, but it works!
Here is my solution for day #19:
const [rawRules, input] = rawInput.split('\n\n') const rules = rawRules .split('\n') .map((rule) => rule.split(': ')) .map((rule) => { return { id: rule[0], possibilities: rule[1], } }) .reduce((acc, rule) => { acc[rule.id] = rule return acc }, {}) function transformToRegex(rules, possibilities) { if (possibilities === '42 | 42 8') return `(${transformToRegex(rules, rules[42].possibilities)})+` return possibilities .split(' | ') .map((possibility) => { return possibility .split(' ') .map((p) => { if (p.match(/\".+\"/)) return p.slice(1, -1) const expression = transformToRegex(rules, rules[p].possibilities) return expression.includes('|') ? `(${expression})` : expression }) .join('') }) .join('|') } const rule11Part1 = transformToRegex(rules, '42') const rule11Part2 = transformToRegex(rules, '31') let rule11 = `${rule11Part1}${rule11Part2}` for (let i = 0; i < 20; i++) { rule11 = `${rule11Part1}(${rule11})?${rule11Part2}` } const firstRegex = transformToRegex(rules, rules[8].possibilities) const fullRegex = new RegExp(`^${firstRegex}${rule11}$`) console.log(input.split('\n').filter((str) => str.match(fullRegex)).length) Feel free to share your solution in the comments!
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