Day 10

day10.peggy

@@ -0,0 +1,6 @@
+lines = line+
+line = @num+ "\n"
+
+num
+  = n:$[0-9] { return parseInt(n, 10) }
+  / '.' { return -1 }

day10.ts

@@ -0,0 +1,57 @@
+import { Point, PointSet, Rect } from './lib/rect.ts';
+import { type MainArgs, parseFile } from './lib/utils.ts';
+
+type Parsed = number[][];
+
+function hike(r: Rect<number>, p: Point, next: number, peaks: PointSet): void {
+  for (const n of p.cardinal(r)) {
+    if (r.get(n) === next) {
+      if (next === 9) {
+        peaks.add(n);
+      } else {
+        hike(r, n, next + 1, peaks);
+      }
+    }
+  }
+}
+
+function hike2(r: Rect<number>, p: Point, next: number): number {
+  // I expected to have to memoize or work from the back to get a solution
+  // that worked fast enough.
+  let count = 0;
+  for (const n of p.cardinal(r)) {
+    if (r.get(n) === next) {
+      if (next === 9) {
+        count++;
+      } else {
+        count += hike2(r, n, next + 1);
+      }
+    }
+  }
+  return count;
+}
+
+function part1(inp: Parsed): number {
+  const r = new Rect(inp);
+  let tot = 0;
+  for (const p of r.filter(v => v === 0)) {
+    const peaks = new PointSet();
+    hike(r, p, 1, peaks);
+    tot += peaks.size;
+  }
+  return tot;
+}
+
+function part2(inp: Parsed): number {
+  const r = new Rect(inp);
+  let tot = 0;
+  for (const p of r.filter(v => v === 0)) {
+    tot += hike2(r, p, 1);
+  }
+  return tot;
+}
+
+export default async function main(args: MainArgs): Promise<[number, number]> {
+  const inp = await parseFile<Parsed>(args);
+  return [part1(inp), part2(inp)];
+}

lib/rect.ts

@@ -124,7 +124,7 @@ export class Point implements PointLike {
     return (this.x === p.x) && (this.y === p.y);
   }
 
-  cardinal(r?: Rect): Point[] {
+  cardinal<T>(r?: Rect<T>): Point[] {
     const ret: Point[] = [];
     for (const [dx, dy] of Point.CARDINAL) {
       const p = this.xlate(dx, dy);