diff --git a/2024/09/solution.js b/2024/09/solution.js
new file mode 100644
index 0000000..4cba1bf
--- /dev/null
+++ b/2024/09/solution.js
@@ -0,0 +1,55 @@
+
+const input = (await Bun.file("input.txt").text()).trim()
+
+// const input = "12345";
+
+const files = [];
+
+const spaces = [];
+
+let pos = 0;
+for (let i = 0; i < input.length; i++ ) {
+  const size = parseInt(input[i])
+  if (i % 2 == 0) {
+    files.push({size, id: i / 2, start: pos,})
+  } else {
+    spaces.push({size, start: pos})
+  }
+  pos += size;
+}
+
+const inserted = [];
+
+let j = 0;
+let end;
+for (let i = files.length - 1; j < spaces.length; i--) {
+  const file = files[i];
+
+  let rem = file.size;
+  while (rem > 0) {
+    const space = spaces[j];
+    if (space.start > file.start) {
+      end = file.start + file.size;
+      break;
+    };
+    const amt = Math.min(space.size, files[i].size)
+
+    spaces[j] = {size: space.size - amt, start: space.start + amt};
+    inserted.push({id: file.id, start: space.start, size: amt,})
+    files[i] = {id: file.id, start: file.start, size: files[i].size - amt,};
+    rem -= amt;
+
+    if (amt == space.size) j++
+  }
+
+  if (end) break
+}
+
+const newfiles = files.concat(inserted)
+  .filter(file => file.size > 0)
+  .sort((a, b) => a.start > b.start)
+
+const checksum = newfiles.reduce((acc, current) => acc + (current.id * current.size * (current.start + (current.size - 1) / 2)), 0)
+
+console.log(checksum)
+