day 9 part 2 wasn't as bad as I thought

09/index.ts

@@ -48,9 +48,90 @@ console.log(
   printTime(now.instant().since(timer))
 );
 
-// timer = now.instant();
-// console.log(
-//   "part two:",
-//   data.split("\n").slice(0, -1),
-//   printTime(now.instant().since(timer))
-// );
+timer = now.instant();
+
+let spaces: Record<string, number[]> = {
+  1: [],
+  2: [],
+  3: [],
+  4: [],
+  5: [],
+  6: [],
+  7: [],
+  8: [],
+  9: [],
+};
+
+sparceArray = 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
+    if (fill === -1 && curr !== 0) {
+      // memoize where all the gaps are, and their sizes
+      spaces[curr].push(disk.length);
+    }
+    return [...disk, ...Array.from({ length: curr }, () => fill)];
+  }, [] as Array<number>);
+
+rightCursor = sparceArray.length - 1;
+while (rightCursor > 0) {
+  if (sparceArray[rightCursor] === -1) {
+    rightCursor--;
+    continue;
+  }
+  let currentFileToMove = sparceArray[rightCursor];
+  let endOfFile = rightCursor;
+  while (sparceArray[rightCursor - 1] === currentFileToMove) {
+    rightCursor--;
+  }
+  let fileSize = endOfFile - rightCursor + 1;
+  // find a slot, if it exists
+  let target = Object.entries(spaces).reduce(
+    (target, [size, spaceList]) => {
+      if (toNum(size) >= fileSize) {
+        if (spaceList[0] < target.index) {
+          return { index: spaceList[0], size };
+        }
+      }
+      return target;
+    },
+    { index: Infinity, size: "" }
+  );
+  if (target.index < Infinity && target.index < rightCursor) {
+    // slot exists; move the file, update the array, and update the space lists
+    sparceArray.splice(
+      target.index,
+      fileSize,
+      ...sparceArray.slice(rightCursor, rightCursor + fileSize)
+    );
+    sparceArray.splice(
+      rightCursor,
+      fileSize,
+      ...Array.from({ length: fileSize }, () => -1)
+    );
+    spaces[target.size].shift();
+    if (toNum(target.size) - fileSize > 0) {
+      spaces[(toNum(target.size) - fileSize).toString()].unshift(
+        target.index + fileSize
+      );
+      spaces[(toNum(target.size) - fileSize).toString()].sort((a, b) =>
+        a > b ? 1 : -1
+      );
+    }
+  }
+  rightCursor--;
+}
+
+console.log(
+  "part two:",
+  sparceArray.reduce((checksum, curr, i) => {
+    if (curr !== -1) {
+      return checksum + curr * i;
+    }
+    return checksum;
+  }, 0),
+  printTime(now.instant().since(timer))
+);