part2.ts

import * as fs from 'fs';
const input = fs
	.readFileSync('input', 'utf8')
	.split('\n')
	.map((x) => x.split(''));

const rows = input.length;
const columns = input[0].length;
const shifts = [
	[-1, 0],
	[0, 1],
	[1, 0],
	[0, -1],
]; // up, right, down, left
const entryPoints = [
	...input[0]
		.map((_, i, r) => [
			{ row: 0, column: i, direction: 2 },
			{ row: r.length - 1, column: i, direction: 0 },
		])
		.flat(),
	...input
		.map((x, i) => [
			{ row: i, column: 0, direction: 1 },
			{ row: i, column: x.length - 1, direction: 3 },
		])
		.flat(),
];

let result = 0;

for (const entryPoint of entryPoints) {
	const checked = {};
	const energized = Array(rows)
		.fill(0)
		.map(() => Array(columns).fill('.'));
	const queue = [entryPoint];

	while (queue.length > 0) {
		const { row, column, direction } = queue.pop();
		const key = [row, column, direction].join(',');
		if (checked[key]) continue;
		checked[key] = true;
		if (row >= 0 && row < rows && column >= 0 && column < columns) {
			energized[row][column] = '#';
			const directions = [];
			switch (input[row][column]) {
				case '|':
					if (direction % 2) directions.push(0, 2);
					else directions.push(direction);
					break;
				case '-':
					if (!(direction % 2)) directions.push(1, 3);
					else directions.push(direction);
					break;
				case '/':
					directions.push(direction ^ 1);
					break;
				case '\\':
					directions.push(direction ^ 3);
					break;
				default:
					directions.push(direction);
					break;
			}
			for (const direction of directions) {
				queue.push({
					row: row + shifts[direction][0],
					column: column + shifts[direction][1],
					direction: direction,
				});
			}
		}
	}

	result = Math.max(result, energized.flat().filter((x) => x === '#').length);
}

console.log(result);