diff --git a/src/day9.rs b/src/day9.rs
index fe0e366..0a39f1c 100644
--- a/src/day9.rs
+++ b/src/day9.rs
@@ -2,17 +2,98 @@ pub fn day9_part1(input: &str) -> String {
     let diskmap = parse(input);
     let mut blocks = diskmap_to_blocks(&diskmap);
     compact(&mut blocks);
-    let sum = blocks
-        .into_iter()
-        .flatten()
-        .enumerate()
-        .map(|(index, block)| index as u64 * block)
-        .sum::<u64>();
+    let sum = checksum(&blocks);
     sum.to_string()
 }
 
 pub fn day9_part2(input: &str) -> String {
-    todo!()
+    let diskmap = parse(input);
+    let compacted_diskmap = defrag_compact(&diskmap);
+    let blocks = compacted_diskmap_to_blocks(&compacted_diskmap);
+    let sum = checksum(&blocks);
+    sum.to_string()
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+struct File {
+    id: u64,
+    length: usize,
+    free_space: usize,
+}
+
+fn compacted_diskmap_to_blocks(compacted_diskmap: &[File]) -> Vec<Option<u64>> {
+    compacted_diskmap
+        .iter()
+        .flat_map(|file| {
+            [
+                vec![Some(file.id); file.length],
+                vec![None; file.free_space],
+            ]
+        })
+        .flatten()
+        .collect()
+}
+
+fn defrag_compact(diskmap: &[usize]) -> Vec<File> {
+    let files = diskmap_to_files(diskmap);
+    let mut compacted_files = files.clone();
+
+    for file in files.clone().into_iter().rev() {
+        let Some(insertable_index) = compacted_files
+            .iter()
+            .enumerate()
+            .find(|(_, insertable_file)| insertable_file.free_space >= file.length)
+            .map(|(i, _)| i)
+        else {
+            continue;
+        };
+
+        let prev_free_space = compacted_files[insertable_index].free_space;
+        compacted_files[insertable_index].free_space = 0;
+        compacted_files.insert(insertable_index + 1, file);
+        compacted_files[insertable_index + 1].free_space = prev_free_space - file.length;
+
+        let nullable_index = compacted_files
+            .iter()
+            .enumerate()
+            .rev()
+            .find(|(_, nullable_file)| nullable_file.id == file.id)
+            .map(|(i, _)| i)
+            .unwrap();
+        compacted_files[nullable_index - 1].free_space +=
+            compacted_files[nullable_index].length + compacted_files[nullable_index].free_space;
+        compacted_files.remove(nullable_index);
+    }
+
+    compacted_files
+}
+
+fn diskmap_to_files(diskmap: &[usize]) -> Vec<File> {
+    let mut id = 0u64;
+    let mut blocks = vec![];
+
+    for digit in diskmap {
+        if id % 2 == 0 {
+            blocks.push(File {
+                id: id / 2,
+                length: *digit,
+                free_space: 0,
+            });
+        } else {
+            blocks.last_mut().unwrap().free_space = *digit;
+        }
+        id += 1
+    }
+
+    blocks
+}
+
+fn checksum(blocks: &[Option<u64>]) -> u64 {
+    blocks
+        .iter()
+        .enumerate()
+        .map(|(index, block)| if let Some(block) = block {index as u64 * block} else {0})
+        .sum::<u64>()
 }
 
 fn diskmap_to_blocks(diskmap: &[usize]) -> Vec<Option<u64>> {
diff --git a/src/lib.rs b/src/lib.rs
index 8b9d499..9bd26be 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -357,13 +357,13 @@ mod tests {
         let result = day9::day9_part1(include_str!("../input/day9.txt"));
         assert_eq!(result, "6448989155953");
     }
-    // #[test]
-    // fn day9_part2_test() {
-    //     let test_result = day9::day9_part2(include_str!("../input/day9.test.txt"));
-    //     assert_eq!(test_result, "34");
-    //     // let result = day9::day9_part2(include_str!("../input/day9.txt"));
-    //     // assert_eq!(result, "1169");
-    // }
+    #[test]
+    fn day9_part2_test() {
+        let test_result = day9::day9_part2(include_str!("../input/day9.test.txt"));
+        assert_eq!(test_result, "2858");
+        let result = day9::day9_part2(include_str!("../input/day9.txt"));
+        assert_eq!(result, "6476642796832");
+    }
 
     #[test]
     fn day8_part1_test() {