Merge pull request #26 from hildjj/day12

Day 12

day12.peggy

@@ -0,0 +1,2 @@
+lines = (@[a-z]i+ "\n")*
+

day12.ts

@@ -0,0 +1,114 @@
+import { BoxDir, Point, PointSet, Rect } from './lib/rect.ts';
+import { type MainArgs, parseFile } from './lib/utils.ts';
+
+type Parsed = string[][];
+
+function flood(
+  r: Rect,
+  val: string,
+  p: Point,
+  visited: PointSet,
+  found: PointSet,
+): number {
+  if (visited.has(p)) {
+    return 0;
+  }
+  visited.add(p);
+  found.add(p);
+  let count = 4;
+  for (const q of p.cardinal(r)) {
+    if (r.get(q) === val) {
+      count--; // Once from each side
+      count += flood(r, val, q, visited, found);
+    }
+  }
+  return count;
+}
+
+function part1(inp: Parsed): number {
+  const r = new Rect(inp);
+  const visited = new PointSet();
+  let tot = 0;
+  r.forEach((v, x, y) => {
+    const found = new PointSet();
+    const p = new Point(x, y);
+    const perim = flood(r, v, p, visited, found);
+    if (found.size > 0) {
+      tot += found.size * perim;
+    }
+  });
+  return tot;
+}
+
+function sides(found: PointSet): number {
+  // Number of sides = number of corners
+
+  // This code could be compressed and sped up by creating a table with 256
+  // entries. Left as an exercise.
+
+  let tot = 0;
+  for (const p of found) {
+    const box = p.boxSet(found);
+    if (!box.has(BoxDir.N) && !box.has(BoxDir.W)) {
+      // ..  X.
+      // .X  .X
+      tot++;
+    } else if (!box.has(BoxDir.NW) && box.has(BoxDir.N) && box.has(BoxDir.W)) {
+      // .X
+      // XX
+      tot++;
+    }
+
+    if (!box.has(BoxDir.N) && !box.has(BoxDir.E)) {
+      // ..  .X
+      // X.  X.
+      tot++;
+    } else if (!box.has(BoxDir.NE) && box.has(BoxDir.N) && box.has(BoxDir.E)) {
+      // X.
+      // XX
+      tot++;
+    }
+
+    if (!box.has(BoxDir.S) && !box.has(BoxDir.E)) {
+      // X.  X.
+      // ..  .X
+      tot++;
+    } else if (!box.has(BoxDir.SE) && box.has(BoxDir.S) && box.has(BoxDir.E)) {
+      // XX
+      // X.
+      tot++;
+    }
+
+    if (!box.has(BoxDir.S) && !box.has(BoxDir.W)) {
+      // .X  .X
+      // ..  X.
+      tot++;
+    } else if (!box.has(BoxDir.SW) && box.has(BoxDir.S) && box.has(BoxDir.W)) {
+      // XX
+      // .X
+      tot++;
+    }
+  }
+
+  return tot;
+}
+
+function part2(inp: Parsed): number {
+  const r = new Rect(inp);
+  const visited = new PointSet();
+  let tot = 0;
+  r.forEach((v, x, y) => {
+    const found = new PointSet();
+    const p = new Point(x, y);
+    flood(r, v, p, visited, found);
+    if (found.size > 0) {
+      tot += found.size * sides(found);
+    }
+  });
+  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

@@ -138,17 +138,42 @@ export class Point implements PointLike {
     return ret;
   }
 
-  *box(r?: Rect): Generator<[Point, BoxDir], undefined, undefined> {
+  *box(r?: Rect | PointSet): 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)) {
+      if (r && !r.has(p)) {
         continue;
       }
       yield [p, dir];
     }
   }
 
+  boxMap(r?: Rect | PointSet): Map<BoxDir, Point> {
+    const ret = new Map<BoxDir, Point>();
+    for (const dir of AllBoxDirs) {
+      const [dx, dy] = Point.BOX[dir];
+      const p = this.xlate(dx, dy);
+      if (r && !r.has(p)) {
+        continue;
+      }
+      ret.set(dir, p);
+    }
+    return ret;
+  }
+
+  boxSet(r: Rect | PointSet): Set<BoxDir> {
+    const ret = new Set<BoxDir>();
+    for (const dir of AllBoxDirs) {
+      const [dx, dy] = Point.BOX[dir];
+      const p = this.xlate(dx, dy);
+      if (r.has(p)) {
+        ret.add(dir);
+      }
+    }
+    return ret;
+  }
+
   toString(): string {
     return `${this.x},${this.y}`;
   }
@@ -266,6 +291,10 @@ export class Rect<T = string> {
       (x >= 0) && (x < this.#vals[y].length);
   }
 
+  has(p: PointLike): boolean {
+    return this.check(p);
+  }
+
   /**
    * Assume that the rectangle is uniform, so the length of the first row
    * is the width.

test/day12.js

@@ -0,0 +1 @@
+export default [1371306, 805880];