Solve 2025-07

2025/07/index.ts

@@ -0,0 +1,51 @@
+import { MultiMap } from '../../utils/multi-map.ts';
+
+export function solveFirst(input: string): number {
+  const rows = input.split('\n');
+  const start = rows[0].indexOf('S');
+
+  const beams = new Set([start]);
+
+  let splits = 0;
+  for (let y = 1; y < rows.length; y++) {
+    const newBeams: number[] = [];
+    beams.forEach((beam) => {
+      if (rows[y][beam] === '.' || beam >= rows[y].length) {
+        return;
+      }
+      if (rows[y][beam] === '^') {
+        splits++;
+        beams.delete(beam);
+        newBeams.push(beam - 1);
+        newBeams.push(beam + 1);
+      }
+    });
+    newBeams.forEach((b) => beams.add(b));
+  }
+
+  return splits;
+}
+
+export function solveSecond(input: string): number {
+  const rows = input.split('\n');
+  const start = rows[0].indexOf('S');
+
+  return solveDown(rows, 1, start);
+}
+
+const cache = new MultiMap<number, [number, number]>();
+function solveDown(map: string[], startY: number, startX: number): number {
+  if (cache.multiHas(startY, startX)) {
+    return cache.multiGet(startY, startX)!;
+  }
+  for (let y = startY; y < map.length; y++) {
+    if (map[y][startX] === '^') {
+      return cache.multiSet(
+        solveDown(map, y + 1, startX - 1) + solveDown(map, y + 1, startX + 1),
+        startY,
+        startX
+      );
+    }
+  }
+  return 1;
+}