index.ts

import run from 'aocrunner'
import * as util from '../utils/index.js'

const parseInput = (rawInput: string) =>
	rawInput
		.trim()
		.split('')
		.map((dir) => (dir === '>' ? 1 : -1)) as (-1 | 1)[]

const ROCKS = [
	{ shape: ['####'], width: 4, height: 1 },
	{ shape: ['.#.', '###', '.#.'], width: 3, height: 3 },
	{ shape: ['..#', '..#', '###'].reverse(), width: 3, height: 3 },
	{ shape: ['#', '#', '#', '#'], width: 1, height: 4 },
	{ shape: ['##', '##'], width: 2, height: 2 },
] as const

const getRockShape = function* (rock: typeof ROCKS[number]) {
	for (let ry = 0; ry < rock.height; ry++) {
		for (let rx = 0; rx < rock.width; rx++) {
			if (rock.shape[ry][rx] !== '#') continue
			yield [rx, ry]
		}
	}
}

const moveRock = (
	leftEdge: number,
	bottomEdge: number,
	down: 0 | 1,
	wind: -1 | 0 | 1,
	rock: typeof ROCKS[number],
	map: (1 | undefined)[][]
) => {
	if (wind === -1 && leftEdge === 0) return false
	if (wind === 1 && leftEdge + rock.width >= 7) return false
	const nextBottom = bottomEdge - down
	const nextSide = leftEdge + wind
	if (nextBottom === 0) return false
	for (const [rx, ry] of getRockShape(rock)) {
		const mapX = nextSide + rx
		const mapY = nextBottom + ry
		if (map[mapY] && map[mapY][mapX]) {
			return false
		}
	}
	return true
}

const commitRock = (
	leftEdge: number,
	bottomEdge: number,
	rock: typeof ROCKS[number],
	map: (1 | undefined)[][]
) => {
	for (const [rx, ry] of getRockShape(rock)) {
		if (rock.shape[ry][rx] !== '#') continue
		const mapX = leftEdge + rx
		const mapY = bottomEdge + ry
		if (!map[mapY]) map[mapY] = []
		map[mapY][mapX] = 1
	}
}

const part1 = (rawInput: string) => {
	const input = parseInput(rawInput)
	let w = 0
	let highestPoint = 0
	let map: (1 | undefined)[][] = []
	for (let r = 0; r < 2022; r++) {
		const rock = ROCKS[r % ROCKS.length]
		let leftEdge = 2
		let bottomEdge = highestPoint + 4
		while (true) {
			const wind = input[w++ % input.length]
			if (moveRock(leftEdge, bottomEdge, 0, wind, rock, map)) {
				leftEdge += wind
			}
			if (moveRock(leftEdge, bottomEdge, 1, 0, rock, map)) {
				bottomEdge--
			} else {
				commitRock(leftEdge, bottomEdge, rock, map)
				const topEdge = bottomEdge + rock.height - 1
				if (topEdge > highestPoint) highestPoint = topEdge
				break
			}
		}
	}
	return highestPoint.toString()
}

const part2 = (rawInput: string) => {
	const input = parseInput(rawInput)
	const windLoop = input.length * 5
	let w = 0
	let highestPoint = 0
	let map: (1 | undefined)[][] = []
	let heightAtLastLoop = 0
	let rocksAtLastLoop = 0
	let loopHeightDelta = 0
	let skippedHeight = 0
	let lastW = 0
	let windLooped = false
	const ROCK_TOTAL = 1000000000000
	for (let r = 0; r < ROCK_TOTAL; r++) {
		if (skippedHeight === 0 && windLooped && r % 5 === 0) {
			windLooped = false
			const newHeight = highestPoint
			if (r > 0 && loopHeightDelta === newHeight - heightAtLastLoop) {
				const rocksPerLoop = r - rocksAtLastLoop
				const loopsLeft = Math.floor((ROCK_TOTAL - r) / rocksPerLoop)
				r += rocksPerLoop * loopsLeft
				skippedHeight = loopHeightDelta * loopsLeft
			} else {
				loopHeightDelta = newHeight - heightAtLastLoop
			}
			heightAtLastLoop = newHeight
			rocksAtLastLoop = r
		}
		const rock = ROCKS[r % ROCKS.length]
		let leftEdge = 2
		let bottomEdge = highestPoint + 4
		while (true) {
			const wind = input[w % input.length]
			w = (w + 1) % windLoop
			if (w === 0) windLooped = true
			lastW = w
			if (moveRock(leftEdge, bottomEdge, 0, wind, rock, map)) {
				leftEdge += wind
			}
			if (moveRock(leftEdge, bottomEdge, 1, 0, rock, map)) {
				bottomEdge--
			} else {
				commitRock(leftEdge, bottomEdge, rock, map)
				const topEdge = bottomEdge + rock.height - 1
				if (topEdge > highestPoint) highestPoint = topEdge
				break
			}
		}
	}
	return (highestPoint + skippedHeight).toString()
}

run({
	part1: {
		tests: [
			{
				input: `>>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>`,
				expected: '3068',
			},
		],
		solution: part1,
	},
	part2: {
		tests: [
			{
				input: `>>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>`,
				expected: '1514285714288',
			},
		],
		solution: part2,
	},
	trimTestInputs: true,
	// onlyTests: true,
})