Day 9 part 2

2024/Day_09/part_2.js

@@ -8,16 +8,40 @@ const __dirname = path.dirname(fileURLToPath(import.meta.url));
 // = Copyright (c) NullDev = //
 // ========================= //
 
-const INPUT = String(fs.readFileSync(path.join(__dirname, "input.txt"))).trim().split("\n");
+/* eslint-disable no-param-reassign, one-var */
+
+const INPUT = String(fs.readFileSync(path.join(__dirname, "input.txt"))).trim().split("");
 
 const pStart = performance.now();
 
-//
-// YOUR CODE HERE
-//
-const result = "...";
+const raw = INPUT.flatMap((bc, i) => Array.from({ length: Number(bc) }, () => (i % 2 ? "." : i / 2)));
+
+const swapBlk = (size) => (l, r) => Array.from({ length: size }, (_, i) => i) // @ts-ignore
+        .forEach(i => ([raw[l + i], raw[r - i]] = [raw[r - i], raw[l + i]])),
+    runs = (idx, rev = false, blk = raw[idx], cnt = 0) => {
+        for (let i = idx; raw[i] === blk; i += rev ? -1 : 1) cnt += 1;
+        return cnt;
+    };
+
+// @ts-ignore
+const hi = raw.findLast((blk) => blk !== ".");
+for (let nxId = hi; nxId >= 0; nxId -= 1){
+    const end = raw.lastIndexOf(nxId), len = runs(end, true), gaps = [];
+    for (let i = 0; i < end; i += 1){
+        if (raw[i] === "."){
+            const gLen = runs(i);
+            gaps.push({ start: i, length: gLen }) && (i += gLen - 1);
+        }
+    }
+
+    const pass = gaps.find((gap) => gap.length >= len);
+    pass && swapBlk(len)(pass.start, end);
+}
+
+// @ts-ignore
+const res = raw.reduce((total, nxId, i) => (total + (nxId === "." ? 0 : nxId * i)), 0);
 
 const pEnd = performance.now();
 
-console.log("<DESCRIPTION>: " + result);
+console.log("NEW FS CHECKSUM: " + res);
 console.log(pEnd - pStart);