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!
Photo by Markus Spiske on Unsplash
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