there's an off-by-one error in here somewhere

09/index.ts

@@ -0,0 +1,50 @@
+import fs from "node:fs";
+import { printTime, now, toNum } from "../util";
+
+const test = true;
+
+const data = fs.readFileSync(
+  test ? "./inputs/testinput" : "./inputs/input",
+  "utf8"
+);
+
+let timer = now.instant();
+console.log(
+  "part one:",
+  data
+    .split("\n")
+    .slice(0, -1)[0]
+    .split("")
+    .map(toNum)
+    .reduce((disk, curr, index) => {
+      const fill = index % 2 === 0 ? index / 2 : -1; // -1 represents free space
+      return [...disk, ...Array.from({ length: curr }, () => fill)];
+    }, [] as Array<number>)
+    .reduce((disk, current, i, a) => {
+      console.log(disk, current, i, a);
+      if (current === -1) {
+        while (true) {
+          let tail = a.pop();
+          if (tail === -1 || tail === undefined) {
+            continue;
+          } else {
+            return [...disk, tail];
+          }
+        }
+      } else {
+        return [...disk, current];
+      }
+    }, [] as Array<number>)
+    .reduce((checksum, curr, i) => {
+      console.log(curr, i);
+      return checksum + curr * i;
+    }, 0),
+  printTime(now.instant().since(timer))
+);
+
+// timer = now.instant();
+// console.log(
+//   "part two:",
+//   data.split("\n").slice(0, -1),
+//   printTime(now.instant().since(timer))
+// );