[TASK] Implemented Day 9

functions/src/day9.ts

@@ -0,0 +1,122 @@
+import Day from "./day";
+import Vector2 from "./vector2";
+import Utils from "./utils";
+
+class Day9 implements Day {
+
+  part1(input: string[]): number | string {
+
+    const heightMap = HeightMap.parseInput(input);
+    const lowPoints = heightMap.findLowPoints();
+    return Utils.sum(lowPoints.map(lp => heightMap.height(lp.x, lp.y) + 1));
+  }
+
+  part2(input: string[]): number | string {
+
+    const heightMap = HeightMap.parseInput(input);
+    const basins = heightMap.findBasins();
+    basins.sort((a, b) => b.size - a.size);
+
+    return basins[0].size * basins[1].size * basins[2].size;
+  }
+
+}
+
+class HeightMap {
+
+  readonly heightMap: number[];
+  readonly width: number;
+  readonly maxY: number;
+
+  constructor(heightMap: number[], width: number) {
+    this.heightMap = heightMap;
+    this.width = width;
+    this.maxY = this.heightMap.length / width;
+  }
+
+  static parseInput(input: string[]): HeightMap {
+
+    const width = input[0].length;
+    const heightMap = [];
+    for (const line of input) {
+      if (line.length !== width) {
+        throw Error("Invalid input");
+      }
+
+      heightMap.push(...line.split("").map(s => parseInt(s)));
+    }
+
+    return new HeightMap(heightMap, width);
+
+  }
+
+  height(x: number, y: number): number {
+    if (x < 0 || x >= this.width || y < 0 || y >= this.maxY) return 9;
+    return this.heightMap[x + y * this.width];
+  }
+
+  findLowPoints(): Vector2[] {
+
+    const res = [];
+    for (let y = 0; y < this.maxY; y++) {
+      for (let x = 0; x < this.width; x++) {
+        if (this.isLowPoint(x, y)) {
+          res.push(new Vector2(x, y));
+        }
+      }
+    }
+    return res;
+  }
+
+  isLowPoint(x: number, y: number): boolean {
+
+    const height = this.height(x, y);
+    return height < this.height(x - 1, y) &&
+      height < this.height(x + 1, y) &&
+      height < this.height(x, y - 1) &&
+      height < this.height(x, y + 1);
+  }
+
+  findBasins(): Basin[] {
+
+    const lowPoints = this.findLowPoints();
+
+    // From every low point, we start to grow "upwards" to claim every point that is part of it's basin:
+    const basinIds = Array(this.width * this.maxY).fill(-1);
+    for (let i = 0; i < lowPoints.length; i++) {
+
+      const stack: Vector2[] = [lowPoints[i]];
+
+      while(stack.length > 0) {
+        const pos = stack.pop();
+        if (!pos) {
+          throw Error("Stack is empty?")
+        }
+        const posHeight = this.height(pos.x, pos.y);
+        basinIds[pos.x + pos.y * this.width] = i;
+        // We add all neighbors to the stack that are low enough, and haven't been assigned to a basin:
+        const neighbors = [pos.addX(1), pos.addX(-1), pos.addY(1), pos.addY(-1)];
+        for (const neighbor of neighbors) {
+          const neighborHeight = this.height(neighbor.x, neighbor.y);
+          if (neighborHeight < 9 && neighborHeight > posHeight && basinIds[neighbor.x + neighbor.y * this.width] === -1) {
+            stack.push(neighbor);
+          }
+        }
+      }
+    }
+
+    return lowPoints.map((lp, i) => new Basin(lp, basinIds.filter(b => b === i).length));
+  }
+}
+
+class Basin {
+  readonly lowPoint: Vector2;
+  readonly size: number;
+
+  constructor(lowPoint: Vector2, size: number) {
+    this.lowPoint = lowPoint;
+    this.size = size;
+  }
+}
+
+export default Day9;

functions/src/index.ts

@@ -10,6 +10,7 @@ import Day5 from "./day5";
 import Day6 from "./day6";
 import Day7 from "./day7";
 import Day8 from "./day8";
+import Day9 from "./day9";
 
 
 // // Start writing Firebase Functions
@@ -34,6 +35,7 @@ export const day = {
   6: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day6(), request, response) }),
   7: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day7(), request, response) }),
   8: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day8(), request, response) }),
+  9: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day9(), request, response) }),
 
 }
 

functions/src/vector2.ts

@@ -18,6 +18,14 @@ class Vector2 {
   key(): string {
     return `${this.x},${this.y}`;
   }
+
+  addX(x: number): Vector2 {
+    return new Vector2(this.x + x, this.y);
+  }
+
+  addY(y: number): Vector2 {
+    return new Vector2(this.x, this.y + y);
+  }
 }
 
 export default Vector2;