From 9a42d884d04c713abd6fe09e4090423ed48eb246 Mon Sep 17 00:00:00 2001
From: Seth Etter <sethetter@gmail.com>
Date: Sat, 9 Dec 2023 08:32:10 -0600
Subject: [PATCH] no bueno

---
 2023/day08/part2.ts | 62 ++++++++++++++++++++++++++++++++++-----------
 2023/day08/test.ts  |  2 +-
 2 files changed, 48 insertions(+), 16 deletions(-)

diff --git a/2023/day08/part2.ts b/2023/day08/part2.ts
index d92381e..2ed5325 100644
--- a/2023/day08/part2.ts
+++ b/2023/day08/part2.ts
@@ -1,39 +1,71 @@
 type Node = { L: string; R: string };
+
 type Network = Record<string, Node>;
 
+type Path = {
+  possiblePaths: string[];
+};
+
+//
+
 export function answer(input: string) {
   const [instructions, , ...networkRaw] = input.split("\n");
 
-  const network: Network = networkRaw.reduce((network, line) => {
-    const [id, leftAndRight] = line.split(" = ");
-    const [L, R] = leftAndRight.replaceAll(/[\(\)]/g, "").split(", ");
-    return { ...network, [id]: { L, R } };
-  }, {});
-
-  const paths = Object.keys(network).filter((n) => n.endsWith("A"));
-  return BigInt(
-    paths
-      .map((p) => countSteps(p, network, instructions))
-      .reduce((total, x) => (total *= x), 1),
-  );
+  const parseNetwork = (lines: string[]): Network =>
+    lines.reduce((network, line) => {
+      const [id, leftAndRight] = line.split(" = ");
+      const [L, R] = leftAndRight.replaceAll(/[\(\)]/g, "").split(", ");
+      return { ...network, [id]: { L, R } };
+    }, {});
+
+  const network: Network = parseNetwork(networkRaw);
+
+  // build the paths to X for each starting path
+  // step forward by longest path
+  // new positions are stepSize % pathSize
+
+  const paths = Object.keys(network)
+    .filter((n) => n.endsWith("A"))
+    .map((p) => {
+      const path = buildPath(p, network, instructions);
+      console.log(`plength: ${path.length}, last: ${path[path.length - 1]}`);
+      return { current: path.length - 1, path };
+    });
+
+  const stepSize = Math.max(...paths.map(({ path }) => path.length));
+  let stepTotal = stepSize;
+
+  while (!paths.every((p) => p.path[p.current] === "Z")) {
+    console.log(`step by ${stepSize}`);
+    paths.forEach((p) => {
+      p.current += stepSize;
+      p.current = p.path.length % p.current;
+      console.log(p);
+    });
+    stepTotal += stepSize;
+  }
+
+  return stepTotal;
 }
 
-function countSteps(
+function buildPath(
   start: string,
   network: Network,
   instructions: string,
-): number {
+): string[] {
   let currentNode = start;
   let stepCount = 0;
+  const endingChars = [start[2]];
   while (!currentNode.endsWith("Z")) {
     for (const dir of instructions.split("")) {
       currentNode = network[currentNode][dir as keyof Node];
       stepCount++;
+      endingChars.push(currentNode[2]);
       if (currentNode.endsWith("Z")) break;
     }
   }
 
-  return stepCount;
+  return endingChars;
 }
 
 if (import.meta.main) {
diff --git a/2023/day08/test.ts b/2023/day08/test.ts
index be1c10c..5ced77b 100644
--- a/2023/day08/test.ts
+++ b/2023/day08/test.ts
@@ -41,5 +41,5 @@ Deno.test("part2", () => {
     "22Z = (22B, 22B)",
     "XXX = (XXX, XXX)",
   ].join("\n");
-  assertEquals(p2.answer(examples), BigInt(6));
+  assertEquals(p2.answer(examples), 6);
 });
-- 
2.51.2