day 9 part one finally done

09/index.ts

@@ -1,7 +1,7 @@
 import fs from "node:fs";
 import { printTime, now, toNum } from "../util";
 
-const test = true;
+const test = false;
 
 const data = fs.readFileSync(
   test ? "./inputs/testinput" : "./inputs/input",
@@ -9,9 +9,8 @@ const data = fs.readFileSync(
 );
 
 let timer = now.instant();
-console.log(
-  "part one:",
-  data
+
+let sparceArray = data
   .split("\n")
   .slice(0, -1)[0]
   .split("")
@@ -19,25 +18,32 @@ console.log(
   .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];
+  }, [] as Array<number>);
+
+let rightCursor = sparceArray.length - 1;
+let leftCursor = 0;
+while (leftCursor < rightCursor) {
+  if (sparceArray[leftCursor] === -1) {
+    while (sparceArray[rightCursor] === -1) {
+      rightCursor--;
     }
+    if (leftCursor > rightCursor) {
+      // don't let them overrun each other
+      break;
     }
-      } else {
-        return [...disk, current];
+    sparceArray[leftCursor] = sparceArray[rightCursor];
+    sparceArray[rightCursor] = -1;
   }
-    }, [] as Array<number>)
-    .reduce((checksum, curr, i) => {
-      console.log(curr, i);
+  leftCursor++;
+}
+
+console.log(
+  "part one:",
+  sparceArray.reduce((checksum, curr, i) => {
+    if (curr !== -1) {
       return checksum + curr * i;
+    }
+    return checksum;
   }, 0),
   printTime(now.instant().since(timer))
 );