AoC2025: day 11 part 2

Author: martapanc

2024-2025/src/2025/day11/day11.test.ts

@@ -7,7 +7,7 @@ describe('2025 Day 11', () => {
     });
 
     test('Part 2', async () => {
-        // expect(await part2('testInput1')).toEqual(31);
-        // expect(await part2('input')).toEqual(29379307);
+        expect(await part2('testInput2')).toEqual(2);
+        expect(await part2('input')).toEqual(358564784931864);
     });
 });

2024-2025/src/2025/day11/day11.ts

@@ -6,7 +6,7 @@ export async function part1(inputFile: string) {
 }
 
 export async function part2(inputFile: string) {
-    return await day11(inputFile);
+    return await day11(inputFile, countPathsVia);
 }
 
 async function day11(inputFile: string, calcFn?: (graph: Map<string, string[]>) => number) {
@@ -58,3 +58,36 @@ function parseGraph(lines: string[]): Map<string, string[]> {
     }
     return graph;
 }
+
+function countPathsVia(graph: Map<string, string[]>): number {
+    const required = new Map<string, number>([
+        ["dac", 1],
+        ["fft", 2],
+    ]);
+    const memo = new Map<string, number>();
+    const visiting = new Set<string>();
+
+    const dfs = (node: string, mask: number): number => {
+        const nextMask = mask | (required.get(node) ?? 0);
+        if (node === "out") {
+            return nextMask === 3 ? 1 : 0;
+        }
+        const key = `${node}|${nextMask}`;
+        const cached = memo.get(key);
+        if (cached !== undefined) return cached;
+        if (visiting.has(key)) {
+            return 0;
+        }
+        visiting.add(key);
+        const neighbors = graph.get(node) ?? [];
+        let total = 0;
+        for (const next of neighbors) {
+            total += dfs(next, nextMask);
+        }
+        visiting.delete(key);
+        memo.set(key, total);
+        return total;
+    };
+
+    return dfs("svr", 0);
+}

2024-2025/src/2025/day11/testInput2

@@ -0,0 +1,13 @@
+svr: aaa bbb
+aaa: fft
+fft: ccc
+bbb: tty
+tty: ccc
+ccc: ddd eee
+ddd: hub
+hub: fff
+eee: dac
+dac: fff
+fff: ggg hhh
+ggg: out
+hhh: out