Day 15

day15.peggy

@@ -0,0 +1,16 @@
+{{
+const E = 0;
+const S = 1;
+const W = 2;
+const N = 3;
+}}
+game = @board "\n" @moves
+board = (@[#O@.]+ "\n")+
+
+moves = (@dir+ "\n")+
+
+dir
+  = "<" { return W }
+  / ">" { return E }
+  / "v" { return S }
+  / "^" { return N }

day15.ts

@@ -0,0 +1,174 @@
+import { type MainArgs, parseFile } from './lib/utils.ts';
+import { Dir, Point, PointSet, Rect } from './lib/rect.ts';
+
+type Parsed = [board: string[][], moves: Dir[][]];
+
+function moveBox(r: Rect, p: Point, d: Dir): boolean {
+  const n = p.inDir(d);
+  const target = r.get(n);
+  if (target === '#') {
+    return false;
+  }
+  if (target === 'O') {
+    if (!moveBox(r, n, d)) {
+      return false;
+    }
+  }
+  r.set(n, 'O');
+  r.set(p, '.');
+  return true;
+}
+
+type Move = [p: Point, val: string];
+
+function moveBigBox(
+  r: Rect,
+  p: Point,
+  d: Dir,
+  moves: Move[],
+  visited: PointSet,
+): boolean {
+  if (visited.has(p)) {
+    return true;
+  }
+  visited.add(p);
+  // p is one end of bigBox.
+  if ((d === Dir.E) || (d === Dir.W)) {
+    const skip = p.inDir(d);
+    const n = skip.inDir(d);
+    const target = r.get(n);
+    if (target === '#') {
+      return false;
+    }
+    if (target !== '.') {
+      if (!moveBigBox(r, n, d, moves, visited)) {
+        return false;
+      }
+    }
+    moves.push([n, r.get(skip)]);
+    moves.push([skip, r.get(p)]);
+    moves.push([p, '.']);
+    return true;
+  } else {
+    const pChar = r.get(p);
+    const o = (pChar === '[') ? p.inDir(Dir.E) : p.inDir(Dir.W);
+    if (visited.has(o)) {
+      return true;
+    }
+    visited.add(o);
+    const nP = p.inDir(d);
+    const nO = o.inDir(d);
+    const nPchar = r.get(nP);
+    const nOchar = r.get(nO);
+    if ((nPchar === '#') || (nOchar === '#')) {
+      return false;
+    }
+    if (nPchar !== '.') {
+      if (!moveBigBox(r, nP, d, moves, visited)) {
+        return false;
+      }
+    }
+    if (
+      (pChar !== nPchar) && (nOchar !== '.') &&
+      !moveBigBox(r, nO, d, moves, visited)
+    ) {
+      return false;
+    }
+    moves.push([nP, pChar]);
+    moves.push([nO, r.get(o)]);
+    moves.push([p, '.']);
+    moves.push([o, '.']);
+
+    return true;
+  }
+}
+
+function part1(inp: Parsed): number {
+  const r = new Rect(inp[0]).copy();
+  let [pos] = r.filter((v) => v === '@');
+  for (const line of inp[1]) {
+    for (const d of line) {
+      const next = pos.inDir(d);
+      const target = r.get(next);
+      // Runs into a wall
+      if (target === '#') {
+        // No-op
+      } else if (target === 'O') {
+        // Do box processing
+        if (moveBox(r, next, d)) {
+          r.set(pos, '.');
+          r.set(next, '@');
+          pos = next;
+        }
+      } else {
+        r.set(pos, '.');
+        r.set(next, '@');
+        pos = next;
+      }
+    }
+  }
+
+  let tot = 0;
+  for (const p of r.filter((v) => v === 'O')) {
+    tot += p.y * 100 + p.x;
+  }
+  return tot;
+}
+
+function part2(inp: Parsed): number {
+  // Double-wide
+  const r = new Rect<string>(inp[0].map((row) =>
+    row.flatMap((v) => {
+      switch (v) {
+        case '#':
+          return ['#', '#'];
+        case 'O':
+          return ['[', ']'];
+        case '.':
+          return ['.', '.'];
+        case '@':
+          return ['@', '.'];
+      }
+      throw new Error(`Invalid cell: ${v}`);
+    })
+  ));
+  let [pos] = r.filter((v) => v === '@');
+  const moves: Move[] = [];
+  const visited = new PointSet();
+  for (const line of inp[1]) {
+    for (const d of line) {
+      const next = pos.inDir(d);
+      const target = r.get(next);
+      // Runs into a wall
+      if (target === '#') {
+        // No-op
+      } else if ((target === '[') || (target === ']')) {
+        moves.length = 0;
+        visited.clear();
+        if (moveBigBox(r, next, d, moves, visited)) {
+          for (const [p, val] of moves) {
+            r.set(p, val);
+          }
+          r.set(pos, '.');
+          r.set(next, '@');
+          pos = next;
+        }
+      } else {
+        r.set(pos, '.');
+        r.set(next, '@');
+        pos = next;
+      }
+    }
+  }
+
+  let tot = 0;
+  for (const p of r.filter((v) => v === '[')) {
+    tot += p.y * 100 + p.x;
+  }
+  return tot;
+}
+
+export default async function main(args: MainArgs): Promise<[number, number]> {
+  const inp = await parseFile<Parsed>(args);
+  return [part1(inp), part2(inp)];
+}

test/day15.js

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+export default [1406392, 1429013];