Day Ten, Part One

src/day_ten.test.ts

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+import {getFurthestDistance} from "./day_ten";
+
+describe('Day Ten', () => {
+	it.each([
+		[`.....
+.S-7.
+.|.|.
+.L-J.
+.....`, 4], [
+			`-L|F7
+7S-7|
+L|7||
+-L-J|
+L|-JF`, 4],
+		[`..F7.
+.FJ|.
+SJ.L7
+|F--J
+LJ...`, 8]
+	])('should calculate the number of steps to the exit', (input, expected) => {
+		const result = getFurthestDistance(input);
+		expect(result).toEqual(expected);
+	});
+});

src/day_ten.ts

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+import fs from "fs";
+
+type Grid = Tile[][];
+type Cell = [number, number];
+type Tile = 'S' | 'F' | 'J' | 'L' | '7' | '-' | '|' | '.';
+
+const isTile = (value: string): value is Tile => {
+	return ['S', 'F', 'J', 'L', '7', '-', '|', '.'].includes(value);
+}
+
+const toString = (cell: Cell): string => {
+	return cell.toString();
+}
+
+const getStart = (grid: Grid): Cell => {
+	const row = grid.findIndex(row => row.includes('S'));
+	const col = grid[row].findIndex(cell => cell === 'S');
+	return [row, col];
+}
+
+const getSurrounding = (grid: Grid, [row, col]: Cell): Cell[] => {
+	return ([
+		[row - 1, col],
+		[row + 1, col],
+		[row, col - 1],
+		[row, col + 1],
+		[row - 1, col - 1],
+		[row - 1, col + 1],
+		[row + 1, col - 1],
+		[row + 1, col + 1],
+	] as Cell[]).filter((cell) => {
+		const valid = isValid(grid, cell);
+		const neighbour = neighbours(grid, cell).map(toString);
+
+		return valid && neighbour.includes([row, col].toString());
+	});
+}
+
+const neighbours = (grid: Grid, [row, col]: Cell): Cell[] => {
+	const value = grid[row][col];
+	switch (value) {
+		case 'F':
+			return [
+				[row, col + 1],
+				[row + 1, col],
+			];
+		case 'J':
+			return [
+				[row - 1, col],
+				[row, col - 1]
+			];
+		case 'L':
+			return [
+				[row, col + 1],
+				[row - 1, col]
+			];
+		case '7':
+			return [
+				[row + 1, col],
+				[row, col - 1]
+			];
+		case '-':
+			return [
+				[row, col + 1],
+				[row, col - 1]
+			];
+		case '|':
+			return [
+				[row - 1, col],
+				[row + 1, col]
+			];
+		default:
+			return [];
+	}
+}
+
+const isValid = (grid: Grid, [row, col]: Cell): boolean => {
+	return row >= 0 && row < grid.length && col >= 0 && col < grid[row].length && grid[row][col] !== '.';
+}
+
+export const getFurthestDistance = (input: string): number => {
+	const grid = input.split('\n').map(line => line.split('').filter(isTile));
+
+	const start = getStart(grid);
+	const queue = getSurrounding(grid, start);
+	console.log(start, queue);
+	const visited = new Set<string>([start.toString()]);
+
+	while (queue.length > 0) {
+		const current = queue.shift()!;
+		const next = neighbours(grid, current);
+
+		next.forEach(cell => {
+			if (!visited.has(cell.toString()) && isValid(grid, cell)) {
+				queue.push(cell);
+				visited.add(cell.toString());
+			}
+		});
+	}
+
+	return visited.size / 2;
+}
+
+export const runDayTen = () => {
+	const input = fs.readFileSync('./inputs/day_ten_input.txt', 'utf8').trimEnd();
+	const result = getFurthestDistance(input);
+	console.log(`Day Ten: ${result}`);
+}