Solve 2025-08

2025/08/index.ts

@@ -0,0 +1,51 @@
+import { multBy, uniqueIndexCombinations } from '../../utils/array.ts';
+import { euclideanDistanceSqrtless } from '../../utils/coordinates.ts';
+
+export function solveFirst(input: string, count = 1000): number {
+  const junctions = input
+    .split('\n')
+    .map((row) => row.split(',').map(Number) as [number, number, number]);
+
+  const edges = uniqueIndexCombinations(junctions)
+    .map(
+      ({ aI, bI }) =>
+        [aI, bI, euclideanDistanceSqrtless(junctions[aI], junctions[bI])] as [
+          number,
+          number,
+          number
+        ]
+    )
+    .toSorted((a, b) => a[2] - b[2]);
+
+  const circuits = junctions.map((_, i) => [i]);
+
+  for (let i = 0; i < edges.length; i++) {
+    const [u, v] = edges[i];
+    const circuitU = circuits.find((c) => c.includes(u))!;
+    const circuitV = circuits.find((c) => c.includes(v))!;
+
+    if (i === count)
+      return multBy(
+        circuits.toSorted((a, b) => b.length - a.length).slice(0, 3),
+        (e) => e.length
+      );
+
+    // already in same circuit, ignore
+    if (circuitU === circuitV) continue;
+
+    // merge v into u
+    circuitU.push(...circuitV);
+    circuits.splice(circuits.indexOf(circuitV), 1);
+
+    // end condition for second
+    if (circuits.length === 1) {
+      return junctions[u][0] * junctions[v][0];
+    }
+  }
+
+  return -1;
+}
+
+export function solveSecond(input: string): number {
+  return solveFirst(input, Number.MAX_SAFE_INTEGER);
+}