part2.ts

import * as fs from 'fs';

const input = fs
	.readFileSync('input', 'utf8')
	.split('\n')
	.map((x) => x.split(' ').map((y: string | number, i) => (y = i === 1 ? +y : y)));

const knots = new Array(10).fill(null).map(() => ({ x: 0, y: 0 }));
const visited = new Set([`0,0`]);

for (const [direction, count] of input) {
	for (let i = 0; i < (count as number); i++) {
		if (direction === 'R') knots[0].x++;
		if (direction === 'L') knots[0].x--;
		if (direction === 'D') knots[0].y++;
		if (direction === 'U') knots[0].y--;
		for (let j = 1; j < knots.length; j++) {
			const [head, tail] = [knots[j - 1], knots[j]];
			if (Math.abs(head.x - tail.x) === 2 || Math.abs(head.y - tail.y) === 2) {
				tail.x += Math.sign(head.x - tail.x);
				tail.y += Math.sign(head.y - tail.y);
			}
		}
		visited.add(`${knots[9].x},${knots[9].y}`);
	}
}

console.log(visited.size);