AoC 2024 day 6

// Advent of Code 2024 - Day 6
const fs = require("fs")

const input = fs.readFileSync(__dirname + (process.argv.includes("--test") ? "/test.txt" : "/input.txt"), "utf8")

const parseInput = (rawInput) => {
    return rawInput.split(/\r?\n/).map((r) => r.split(""))
}
const directions = [
    [-1, 0], // up
    [0, 1], // right
    [1, 0], // down
    [0, -1] // left
]
function findStartPosition(map) {
    for (let i = 0; i < map.length; i++) {
        const col = map[i].indexOf("^")
        if (col !== -1) return [i, col] // Return the position as soon as we find '^'
    }
}
const visitedPositions = new Set()

const part1 = (map) => {
    let guardPos = [...guardStartPos]
    let directionIndex = 0

    const rows = map.length
    const cols = map[0].length

    while (true) {
        const [dx, dy] = directions[directionIndex]
        const [x, y] = guardPos
        const nextPos = [x + dx, y + dy]

        if (nextPos[0] < 0 || nextPos[0] >= rows || nextPos[1] < 0 || nextPos[1] >= cols) {
            break
        }

        if (map[nextPos[0]][nextPos[1]] !== "#") {
            visitedPositions.add(nextPos.toString())
            guardPos = nextPos
        } else {
            directionIndex = (directionIndex + 1) % directions.length
        }
    }

    return visitedPositions.size
}

const part2 = (map) => {
    const rows = map.length
    const cols = map[0].length

    const simulateMovement = (modifiedMap) => {
        const visitedStates = new Set()
        let guardPos = [...guardStartPos]
        let directionIndex = 0

        while (true) {
            const [dx, dy] = directions[directionIndex]
            const [x, y] = guardPos
            const nextPos = [x + dx, y + dy]

            if (nextPos[0] < 0 || nextPos[0] >= rows || nextPos[1] < 0 || nextPos[1] >= cols) {
                return false
            }

            if (modifiedMap[nextPos[0]][nextPos[1]] !== "#") {
                const stateKey = `${guardPos}-${directionIndex}`
                if (visitedStates.has(stateKey)) {
                    return true
                }
                visitedStates.add(stateKey)
                guardPos = nextPos
            } else {
                directionIndex = (directionIndex + 1) % directions.length
            }
        }
    }

    let loopCount = 0
    visitedPositions.delete(guardStartPos.toString())
    for (const pos of visitedPositions) {
        const [row, col] = pos.split(",").map(Number)

        const modifiedMap = map.map((row) => [...row])
        modifiedMap[row][col] = "#"

        if (simulateMovement(modifiedMap)) {
            loopCount++
        }
    }

    return loopCount
}

const data = parseInput(input)
let guardStartPos = findStartPosition(data)
console.time("Part 1 Time")
console.log("Part 1:", part1(data))
console.timeEnd("Part 1 Time")

console.time("Part 2 Time")
console.log("Part 2:", part2(data))
console.timeEnd("Part 2 Time")