Day 4

day4.peggy

@@ -0,0 +1 @@
+lines = (@[^\n]+ "\n")*

day4.ts

@@ -0,0 +1,50 @@
+import { type MainArgs, parseFile } from './lib/utils.ts';
+import { AllBoxDirs, BoxDir, Rect } from './lib/rect.ts';
+
+type Parsed = string[][];
+
+function part1(inp: Parsed): number {
+  let tot = 0;
+  const r = new Rect(inp);
+  const Xs = r.filter((v) => v === 'X');
+
+  for (const x of Xs) {
+    for (const dir of AllBoxDirs) {
+      if (r.ray(x, dir, 4).join('') === 'XMAS') {
+        tot++;
+      }
+    }
+  }
+
+  return tot;
+}
+
+function part2(inp: Parsed): number {
+  let tot = 0;
+  const r = new Rect(inp);
+  const As = r.filter((v) => v === 'A');
+
+  const corners = [BoxDir.NW, BoxDir.SE, BoxDir.NE, BoxDir.SW];
+  for (const a of As) {
+    const letters = corners.map((d) => {
+      const p = a.inBoxDir(d, r);
+      return p ? r.get(p) : undefined;
+    });
+    if (letters.some((p) => (p !== 'M') && (p !== 'S'))) {
+      continue;
+    }
+    if (letters[0] === letters[1]) {
+      continue;
+    }
+    if (letters[2] === letters[3]) {
+      continue;
+    }
+    tot++;
+  }
+  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

@@ -26,13 +26,46 @@ export const OppositeDir: Record<Dir, Dir> = {
   [Dir.N]: Dir.S,
 };
 
+export enum BoxDir {
+  NW,
+  N,
+  NE,
+  E,
+  SE,
+  S,
+  SW,
+  W,
+}
+
+export const AllBoxDirs: BoxDir[] = [
+  BoxDir.NW,
+  BoxDir.N,
+  BoxDir.NE,
+  BoxDir.E,
+  BoxDir.SE,
+  BoxDir.S,
+  BoxDir.SW,
+  BoxDir.W,
+];
+
 export class Point implements PointLike {
   static CARDINAL: [dx: number, dy: number][] = [
     [1, 0],
     [0, 1],
     [-1, 0],
     [0, -1],
   ];
+  static BOX: [dx: number, dy: number][] = [
+    [-1, -1],
+    [0, -1],
+    [1, -1],
+    [1, 0],
+    [1, 1],
+    [0, 1],
+    [-1, 1],
+    [-1, 0],
+  ];
+
   x: number;
   y: number;
 
@@ -60,6 +93,15 @@ export class Point implements PointLike {
     return this.xlate(dx, dy);
   }
 
+  inBoxDir<T>(dir: BoxDir, rect?: Rect<T>): Point | undefined {
+    const [dx, dy] = Point.BOX[dir];
+    const p = this.xlate(dx, dy);
+    if (rect && !rect.check(p)) {
+      return undefined;
+    }
+    return p;
+  }
+
   stretch(len: number): Point {
     return new Point(this.x * len, this.y * len);
   }
@@ -88,6 +130,17 @@ export class Point implements PointLike {
     return ret;
   }
 
+  *box(r?: Rect): Generator<[Point, BoxDir], undefined, undefined> {
+    for (const dir of AllBoxDirs) {
+      const [dx, dy] = Point.BOX[dir];
+      const p = this.xlate(dx, dy);
+      if (r && !r.check(p)) {
+        continue;
+      }
+      yield [p, dir];
+    }
+  }
+
   toString(): string {
     return `${this.x},${this.y}`;
   }
@@ -124,6 +177,13 @@ export type RectEachCallback<T> = (
   r: Rect<T>,
 ) => void;
 
+export type RectFilterCallback<T> = (
+  value: T,
+  x: number,
+  y: number,
+  r: Rect<T>,
+) => boolean;
+
 export class Rect<T = string> {
   #vals: T[][];
 
@@ -319,6 +379,30 @@ export class Rect<T = string> {
     return prev;
   }
 
+  filter(callbackFn: RectFilterCallback<T>): Point[] {
+    const res: Point[] = [];
+    this.forEach((v, x, y) => {
+      if (callbackFn(v, x, y, this)) {
+        res.push(new Point(x, y));
+      }
+    });
+    return res;
+  }
+
+  ray(origin: Point, dir: BoxDir, len: number): T[] {
+    const res: T[] = [];
+    let p: Point = origin;
+    for (let i = 0; i < len; i++) {
+      res.push(this.get(p));
+      const q = p.inBoxDir(dir, this);
+      if (!q) {
+        break;
+      }
+      p = q;
+    }
+    return res;
+  }
+
   /**
    * @returns The values in the rect.
    */

test/day4.js

@@ -0,0 +1 @@
+export default [2569, 1998];