day 18 part 2

Author: NullDev

2024/Day_18/part_2.js

@@ -8,16 +8,38 @@ const __dirname = path.dirname(fileURLToPath(import.meta.url));
 // = Copyright (c) NullDev = //
 // ========================= //
 
+/* eslint-disable no-nested-ternary, no-sequences */
+
 const INPUT = String(fs.readFileSync(path.join(__dirname, "input.txt"))).trim().split("\n");
 
 const pStart = performance.now();
 
-//
-// YOUR CODE HERE
-//
-const result = "...";
+const res = ((
+    grid = Array.from({ length: 71 }, () => Array(71).fill(false)),
+    pos = INPUT.map(line => line.split(",").map(s => parseInt(s, 10))),
+    dir = [[0, 1], [0, -1], [1, 0], [-1, 0]],
+) => {
+    const valid = () =>
+        grid[0][0] ? false : ((
+            seen = Array.from({ length: 71 }, () => Array(71).fill(false)),
+        ) => {
+            seen[0][0] = true;
+            const bfs = front =>
+                front.some(({ x, y })=>x === 71 - 1 && y === 71 - 1) ? true : front.length === 0
+                    ? false : bfs(
+                        front.flatMap(({ x, y }) => dir.map(([dx, dy]) => ({ nx: x + dx, ny: y + dy }))
+                            .filter(({ nx, ny }) => (
+                                nx >= 0 && nx < 71 && ny >= 0 && ny < 71 &&
+                                        !grid[ny][nx] && !seen[ny][nx] && (seen[ny][nx] = true)
+                            )).map(({ nx, ny }) => ({ x: nx, y: ny })),
+                        ),
+                    );
+            return bfs([{ x: 0, y: 0 }]);
+        })();
+    return pos.find(([x, y]) => ((grid[y][x] = true), !valid()))?.join(",");
+})();
 
 const pEnd = performance.now();
 
-console.log("<DESCRIPTION>: " + result);
+console.log("MINIMUM NUMBER OF STEPS: " + res);
 console.log(pEnd - pStart);

README.md

@@ -137,6 +137,7 @@ I also tried to experiment with a couple of different things:
 - One-Liner in both [Day_13/part_1.js](https://github.com/NullDev/Advent-of-Code/blob/master/2024/Day_13/part_1.js) and [Day_13/part_2.js](https://github.com/NullDev/Advent-of-Code/blob/master/2024/Day_13/part_2.js)
 - One-Liner in [Day_14/part_1.js](https://github.com/NullDev/Advent-of-Code/blob/master/2024/Day_14/part_1.js)
 - Sloppy, hacky, small, quick & dirty dijkstra in [Day_16/part_1.js](https://github.com/NullDev/Advent-of-Code/blob/master/2024/Day_16/part_1.js)
+- _Almost_ One-Liner [BFS](https://en.wikipedia.org/wiki/Breadth-first_search) in [Day_18/part_1.js](https://github.com/NullDev/Advent-of-Code/blob/master/2024/Day_18/part_1.js)
 
 <hr>