From 835e507816b748da8c37c1ce656c5f36d93668af Mon Sep 17 00:00:00 2001
From: Lewis Dale <lewis.dale@triptease.com>
Date: Mon, 11 Dec 2023 08:58:55 +0000
Subject: [PATCH] Day Eleven

---
 index.ts               |  4 +--
 src/day_eleven.test.ts | 27 +++++++++++++++++
 src/day_eleven.ts      | 66 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 95 insertions(+), 2 deletions(-)
 create mode 100644 src/day_eleven.test.ts
 create mode 100644 src/day_eleven.ts

diff --git a/index.ts b/index.ts
index 3ffc6b4..64fbfdf 100644
--- a/index.ts
+++ b/index.ts
@@ -1,3 +1,3 @@
-import {runDayNine} from "./src/day_nine";
+import {runDayEleven} from "./src/day_eleven";
 
-runDayNine();
\ No newline at end of file
+runDayEleven();
\ No newline at end of file
diff --git a/src/day_eleven.test.ts b/src/day_eleven.test.ts
new file mode 100644
index 0000000..955a59c
--- /dev/null
+++ b/src/day_eleven.test.ts
@@ -0,0 +1,27 @@
+import {Observatory} from "./day_eleven";
+
+describe('Observatory', () => {
+	const input = `...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....`;
+
+	it('should calculate the shortest path between every galaxy', () => {
+		const observatory = new Observatory(input);
+		expect(observatory.shortestPaths).toEqual(82000210);
+	});
+
+	it.each([
+		[[9, 0], [9, 4], 1_000_004],
+		[[0, 3], [8, 7], 3_000_012],
+	])(`should calculate the distance between two galaxies`, (galaxyOne, galaxyTwo, expectedDistance) => {
+		const observatory = new Observatory(input);
+		expect(observatory.distanceBetween(galaxyOne as [number, number], galaxyTwo as [number, number])).toEqual(expectedDistance);
+	});
+});
\ No newline at end of file
diff --git a/src/day_eleven.ts b/src/day_eleven.ts
new file mode 100644
index 0000000..9e810c9
--- /dev/null
+++ b/src/day_eleven.ts
@@ -0,0 +1,66 @@
+import {Range, Seq, Set} from "immutable";
+import fs from "fs";
+
+type Position = [number, number];
+type GalaxyPair = [Position, Position];
+
+export class Observatory {
+	private grid: string[][] = [];
+	private expandedRows: number[] = [];
+	private expandedColumns: number[] = [];
+
+	constructor(input: string) {
+		this.grid = input.split('\n').map(line => line.split(''));
+
+		this.expandGrid();
+	}
+
+	private expandGrid() {
+		this.expandedColumns = Range(0, this.grid[0].length).filter(column => this.grid.every(row => row[column] === '.')).toArray();
+		this.expandedRows = Range(0, this.grid.length).filter(row => this.grid[row].every(column => column === '.')).toArray();
+	}
+
+	public get shortestPaths(): number {
+		const distances = this.pairs.map(pair => this.distanceBetween(pair[0], pair[1]));
+		return distances.reduce((sum, distance) => sum + distance, 0);
+	}
+
+	private get pairs(): GalaxyPair[] {
+		const galaxies = this.grid.reduce((galaxies, row, rowIndex) => {
+			row.forEach((galaxy, columnIndex) => {
+				if (galaxy === '#') {
+					galaxies.push([rowIndex, columnIndex]);
+				}
+			});
+			return galaxies;
+		}, [] as Position[]);
+
+		return galaxies.reduce((pairs, galaxy, index) => {
+			return pairs.withMutations(pairs => {
+				galaxies.slice(index + 1).forEach(otherGalaxy => {
+					pairs.add([galaxy, otherGalaxy]);
+				});
+			})
+		}, Set<GalaxyPair>()).toArray();
+	}
+
+	private range = (a: number, b: number): Seq.Indexed<number> => {
+		return Range(Math.min(a, b), Math.max(a, b) + 1);
+	}
+	public distanceBetween(galaxyOne: Position, galaxyTwo: Position): number {
+		const expansion = 999_999;
+
+		const xRange = this.range(galaxyOne[0], galaxyTwo[0]).filter(row => this.expandedRows.includes(row)).toArray().length;
+		const yRange = this.range(galaxyOne[1], galaxyTwo[1]).filter(column => this.expandedColumns.includes(column)).toArray().length;
+
+		const expansions = expansion * (xRange + yRange)
+
+		return Math.abs(galaxyOne[0] - galaxyTwo[0]) + Math.abs(galaxyOne[1] - galaxyTwo[1]) + expansions;
+	}
+}
+
+export const runDayEleven = () => {
+	const input = fs.readFileSync('./inputs/day_eleven_input.txt', 'utf-8').trimEnd();
+	const observatory = new Observatory(input);
+	console.log(`The shortest path between every galaxy is ${observatory.shortestPaths}`);
+}
\ No newline at end of file