AoC/2024/06/index.ts

const fs = require('fs');

const input = fs.readFileSync(__dirname + '/input.txt', 'utf8');

interface Coord { x: number, y: number };
enum Dir {
    Up,
    Right,
    Down,
    Left
}

const obs: Array<Coord> = [];
let guard: { pos: Coord, dir: Dir } = { pos: { x: 0, y: 0}, dir: Dir.Up };

const keyMap: { [key: string]: (pos: Coord) => any } = {
    "#": (pos: Coord) => obs.push(pos),
    "^": (pos: Coord) => guard = { pos, dir: Dir.Up },
    ">": (pos: Coord) => guard = { pos, dir: Dir.Up },
    "v": (pos: Coord) => guard = { pos, dir: Dir.Up },
    "<": (pos: Coord) => guard = { pos, dir: Dir.Up },
}

let x = 0;
let y = 0;
for (let i = 0; i <= input.length; i++) {
    const char = input[i];
    if (char === "\n") {
        y++;
        x = 0;
        continue;
    }
    if (keyMap[char]) {
        keyMap[char]({ x, y });
    }
    x++;
}
const width = x;
const height = y + 1;
const guardStart = guard.pos;


const positions: Array<Coord> = [guard.pos];

function coordsMatch(a: Coord, b: Coord) {
    return a.x === b.x && a.y === b.y;
}

function getNextPosition() {
    if (guard.dir === Dir.Up) {
        return { x: guard.pos.x, y: guard.pos.y - 1 };
    }
    if (guard.dir === Dir.Right) {
        return { x: guard.pos.x + 1, y: guard.pos.y };
    }
    if (guard.dir === Dir.Down) {
        return { x: guard.pos.x, y: guard.pos.y + 1 };
    }
    return { x: guard.pos.x - 1, y: guard.pos.y };
}

function rotateGuard() {
    if (guard.dir === Dir.Up) {
        guard.dir = Dir.Right;
    } else if (guard.dir === Dir.Right) {
        guard.dir = Dir.Down;
    } else if (guard.dir === Dir.Down) {
        guard.dir = Dir.Left;
    } else {
        guard.dir = Dir.Up;
    }
}

function isObs(coord: Coord, otherObs: Array<Coord>|null = null) {
    return (otherObs || obs).some((obsCoord) => coordsMatch(obsCoord, coord));
}

function offMap(coord: Coord) {
    return coord.x >= width
        || coord.x < 0
        || coord.y >= height
        || coord.y < 0;
}

function alreadyVisited(coord: Coord) {
    return positions.some((pos) => coordsMatch(pos, coord));
}

while (true) {
    const nextPos = getNextPosition();
    if (isObs(nextPos)) {
        rotateGuard();
        continue;
    }
    if (offMap(nextPos)) {
        break;
    }
    guard.pos = nextPos;
    if (!alreadyVisited(nextPos)) {
        positions.push(nextPos);
    }
}

// Part 2
let loops = 0;
positions.slice(1).forEach((pos, i) => {
    console.log(Math.floor(`${i / positions.length * 100}%`));
    guard.pos = guardStart;
    guard.dir = Dir.Up;
    const newObs = [...obs, pos];
    const guardPositions: Array<string> = [];
    while (true) {
        const nextPos = getNextPosition();
        if (isObs(nextPos, newObs)) {
            rotateGuard();
            continue;
        }
        if (offMap(nextPos)) {
            break;
        }
        const guardPos = `${guard.pos.x},${guard.pos.y},${guard.dir}`;
        if (guardPositions.includes(guardPos)) {
            loops++;
            break;
        }
        guardPositions.push(guardPos);
        guard.pos = nextPos;
    }
    x++;
});
// End Part 2

console.log(positions.length);
console.log(loops);