Part 2 done

2024/rust/src/day9.rs

@@ -6,10 +6,20 @@ fn main() {
     show_answers(part1(&input), part2(&input));
 }
 
-fn part1(input: &str) -> usize {
+struct Disk {
+    blocks: Vec<Option<usize>>,
+    files: Vec<(usize, u8)>,
+    free_blocks: usize,
+}
+
+impl FromStr for Disk {
+    type Err = Infallible;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut blocks: Vec<Option<usize>> = vec![];
+        let mut files = vec![];
         let mut free_blocks: usize = 0;
-    for (i, len) in input.trim().bytes().map(|len| len - b'0').enumerate() {
+        for (i, len) in s.trim().bytes().map(|len| len - b'0').enumerate() {
             // every other iteration is "free space"
             let file_id = if i % 2 == 0 {
                 Some((i / 2) as usize)
@@ -17,32 +27,65 @@ fn part1(input: &str) -> usize {
                 free_blocks += len as usize;
                 None
             };
+            if file_id.is_some() {
+                files.push((blocks.len(), len));
+            }
             for _ in 0..len {
                 blocks.push(file_id);
             }
         }
-    println!("{blocks:?}");
-    let mut right = blocks.len() - 1;
-    for left in 0..(right.clone() - free_blocks + 1) {
-        if blocks[left].is_some() {
-            continue;
+        Ok(Self {
+            files,
+            blocks,
+            free_blocks,
+        })
     }
-        while blocks[right].is_none() {
-            right -= 1;
-        }
-        (blocks[left], blocks[right]) = (blocks[right], blocks[left]);
-    }
-    println!("{blocks:?}");
+}
 
-    blocks
+impl Disk {
+    fn checksum(&self) -> usize {
+        self.blocks
             .iter()
             .enumerate()
             .map(|(i, b)| i * b.unwrap_or_default())
             .sum()
+    }
+}
+
+fn part1(input: &str) -> usize {
+    let mut disk: Disk = input.parse().unwrap();
+    let mut right = disk.blocks.len() - 1;
+    for left in 0..(right.clone() - disk.free_blocks + 1) {
+        if disk.blocks[left].is_some() {
+            continue;
+        }
+        while disk.blocks[right].is_none() {
+            right -= 1;
+        }
+        (disk.blocks[left], disk.blocks[right]) = (disk.blocks[right], disk.blocks[left]);
+    }
+
+    disk.checksum()
 }
 
 fn part2(input: &str) -> usize {
-    1
+    let mut disk: Disk = input.parse().unwrap();
+    for (cur_i, len) in disk.files.iter().rev() {
+        for left in 0..*cur_i {
+            if disk.blocks[left..(left + (*len as usize))]
+                .iter()
+                .all(|f| f.is_none())
+            {
+                for i in 0..*len {
+                    let i = i as usize;
+                    (disk.blocks[left + i], disk.blocks[cur_i + i]) =
+                        (disk.blocks[cur_i + i], disk.blocks[left + i])
+                }
+                break;
+            }
+        }
+    }
+    disk.checksum()
 }
 
 #[cfg(test)]
@@ -53,6 +96,6 @@ mod tests {
     fn test() {
         let input = r#"2333133121414131402"#;
         assert_eq!(part1(input), 1928);
-        assert_eq!(part2(input), 1);
+        assert_eq!(part2(input), 2858);
     }
 }