advent of code 2024 chiri solutions day 5

solution.js

const [rulesInput, updatesInput] = input.split("\n\n")

const rules = Object.fromEntries(Object.entries(Object.groupBy(rulesInput.split("\n").map(rule => rule.split("|").map(n => +n)), a => a[1])).map(([page, dependencies]) => [page, dependencies.map(dependency => dependency[0])]))

const dependants = Object.fromEntries(Object.entries(Object.groupBy(rulesInput.split("\n").map(rule => rule.split("|").map(n => +n)), a => a[0])).map(([page, dependants]) => [page, dependants.map(dependant => dependant[1])]))

const updates = updatesInput.split("\n").map(update => update.split(",").map(n => +n))
const { validUpdates, invalidUpdates } = Object.groupBy(updates, update => ruleCheck(update) ? "validUpdates" : "invalidUpdates")
const fixedUpdates = invalidUpdates.map(update => ruleSort(update))

;[sumMiddlePages(validUpdates), sumMiddlePages(fixedUpdates)]

function sumMiddlePages (updates) {
	return updates.map(update => update[Math.floor(update.length / 2)]).reduce((c, v) => c + v, 0)
}

function ruleCheck (update) {
	for (let i = update.length - 1; i > 0; i--)
		for (let c = 0; c < i; c++)
			if (dependants[update[i]].includes(update[c]))
				return false
	return true
}

function ruleSort (update) {
	const loaded = []
	for (const page of update)
		loadPage(page)
	return loaded

	function loadPage (page) {
		if (loaded.includes(page))
			return

		const dependencies = rules[page]
		for (const dependency of dependencies)
			if (update.includes(dependency))
				loadPage(dependency)
		loaded.push(page)
	}
}