Merge pull request #23 from hildjj/day11

Day 11

day11.peggy

@@ -0,0 +1,4 @@
+line = @num|.., _| "\n"
+
+num = n:$[0-9]+ { return parseInt(n, 10) }
+_ = [ \t]+

day11.ts

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+import { type MainArgs, parseFile } from './lib/utils.ts';
+
+type Parsed = number[];
+
+function mapAdd(m: Map<number, number>, k: number, v = 1): void {
+  const se = m.get(k);
+  m.set(k, (se ?? 0) + v);
+}
+
+function blink(inp: Parsed, num: number): number {
+  // Each stone k occurs v times.  On a new iteration, there are a multiple
+  // ways that a given numbered stone might be created.  Add all of those ways.
+  // However, no matter how a stone got created, it will have the same set of
+  // descendants.
+  let prev = new Map<number, number>();
+  for (const s of inp) {
+    mapAdd(prev, s);
+  }
+  for (let i = 0; i < num; i++) {
+    const next = new Map<number, number>();
+    for (const [k, v] of prev) {
+      if (k === 0) {
+        mapAdd(next, 1, v);
+      } else {
+        const ks = String(k);
+        if (ks.length % 2 === 0) {
+          const kl = ks.length / 2;
+          mapAdd(next, Number(ks.slice(0, kl)), v);
+          mapAdd(next, Number(ks.slice(kl)), v);
+        } else {
+          mapAdd(next, k * 2024, v);
+        }
+      }
+    }
+    prev = next;
+  }
+  let count = 0;
+  for (const [_k, v] of prev) {
+    count += v;
+  }
+  return count;
+}
+
+function part1(inp: Parsed): number {
+  return blink(inp, 25);
+}
+
+function part2(inp: Parsed): number {
+  return blink(inp, 75);
+}
+
+export default async function main(args: MainArgs): Promise<[number, number]> {
+  const inp = await parseFile<Parsed>(args);
+  return [part1(inp), part2(inp)];
+}

test/day11.js

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+export default [182081, 216318908621637];