Add solution to 2022/12/24 part 2

2022/24/README.md

@@ -255,3 +255,15 @@ Minute 18, move down:
 
 __What is the fewest number of minutes required to avoid the blizzards and reach the goal?__
 
+## --- Part Two ---
+
+As the expedition reaches the far side of the valley, one of the Elves looks especially dismayed:
+
+He __forgot his snacks__ at the entrance to the valley!
+
+Since you're so good at dodging blizzards, the Elves humbly request that you go back for his snacks. From the same initial conditions, how quickly can you make it from the start to the goal, then back to the start, then back to the goal?
+
+In the above example, the first trip to the goal takes `18` minutes, the trip back to the start takes `23` minutes, and the trip back to the goal again takes `13` minutes, for a total time of `54` minutes.
+
+__What is the fewest number of minutes required to reach the goal, go back to the start, then reach the goal again?__
+

2022/24/main.ts

@@ -1,4 +1,5 @@
 import input from "../../utils/deno/input.ts";
-import { solvePart1 } from "./solutions.ts";
+import { solvePart1, solvePart2 } from "./solutions.ts";
 
 console.log(solvePart1(input));
+console.log(solvePart2(input));

2022/24/solutions.ts

@@ -91,13 +91,14 @@ function mutate(currentMap: string[][]): string[][] {
 function bfs(
   states: string[][][],
   startPosition: Vector,
-  goalPosition: Vector
+  goalPosition: Vector,
+  initialSteps = 0
 ): number {
   const width = states[0][0].length;
   const height = states[0].length;
 
   const toVisit: (Vector & { steps: number; waits: number })[] = [];
-  toVisit.push({ ...startPosition, steps: 0, waits: 0 });
+  toVisit.push({ ...startPosition, steps: initialSteps, waits: 0 });
 
   const visited: Record<string, boolean> = {};
 
@@ -166,3 +167,29 @@ export function solvePart1(input: Input): number {
 
   return bfs(states, startPosition, goalPosition);
 }
+
+export function solvePart2(input: Input): number {
+  const currentMap: string[][] = input.lines.map((x) => x.split(""));
+
+  // Pre-compute blizzard states
+  const states: string[][][] = [currentMap];
+  for (let i = 1; i < 1000; i++) {
+    states.push(mutate(states[i - 1]));
+  }
+
+  const startPosition = {
+    x: currentMap[0].findIndex((x) => x === "."),
+    y: 0,
+  };
+
+  const goalPosition = {
+    x: currentMap[currentMap.length - 1].findIndex((x) => x === "."),
+    y: currentMap.length - 1,
+  };
+
+  const round1 = bfs(states, startPosition, goalPosition);
+  const round2 = bfs(states, goalPosition, startPosition, round1);
+  const round3 = bfs(states, startPosition, goalPosition, round2);
+
+  return round3;
+}

2022/24/test.ts

@@ -1,6 +1,6 @@
 import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
 import { Input } from "../../utils/deno/input.ts";
-import { solvePart1 } from "./solutions.ts";
+import { solvePart1, solvePart2 } from "./solutions.ts";
 
 Deno.test("part 1 - given test case", () => {
   const input = `#.######
@@ -11,3 +11,13 @@ Deno.test("part 1 - given test case", () => {
 ######.#`;
   assertEquals(solvePart1(new Input(input)), 18);
 });
+
+Deno.test("part 2 - given test case", () => {
+  const input = `#.######
+#>>.<^<#
+#.<..<<#
+#>v.><>#
+#<^v^^>#
+######.#`;
+  assertEquals(solvePart2(new Input(input)), 54);
+});