WIP: 9th day

Author: majcn

data/examples/09.txt

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+2333133121414131402

src/bin/09.rs

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+advent_of_code::solution!(9);
+
+#[derive(Debug, Copy, Clone)]
+enum Block {
+    Free,
+    File(usize),
+}
+
+fn parse_data(input: &str) -> Vec<(usize, Block)> {
+    input
+        .bytes()
+        .enumerate()
+        .map(|(i, x)| {
+            if i % 2 == 0 {
+                ((x - b'0') as usize, Block::File(i / 2))
+            } else {
+                ((x - b'0') as usize, Block::Free)
+            }
+        })
+        .collect()
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let data = parse_data(input);
+
+    let mut disk = vec![];
+    let mut id = 0;
+    for (i, x) in data.into_iter().enumerate() {
+        if i % 2 == 0 {
+            for _ in 0..x.0 {
+                disk.push(Block::File(id));
+            }
+            id += 1;
+        } else {
+            for _ in 0..x.0 {
+                disk.push(Block::Free);
+            }
+        }
+    }
+
+    let mut i = 0;
+    let mut j = disk.len() - 1;
+    loop {
+        while let Block::File(_) = disk[i] {
+            i += 1;
+        }
+
+        while let Block::Free = disk[j] {
+            j -= 1;
+        }
+
+        if i > j {
+            break;
+        }
+
+        disk.swap(i, j);
+    }
+
+    let mut result = 0;
+    for (i, block) in disk.iter().enumerate() {
+        if let Block::File(id) = block {
+            result += i as u64 * *id as u64;
+        }
+    }
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let data = parse_data(input);
+
+    let mut disk = data;
+    disk.push((10, Block::Free));
+
+    for j in (0..10000).rev() {
+        let file_index = disk.iter().position(|(_, block)| match block {
+            Block::Free => false,
+            Block::File(x) => *x == j,
+        });
+
+        if file_index.is_none() {
+            continue;
+        }
+
+        let file_index = file_index.unwrap();
+
+        let file_block = disk[file_index].1;
+        let file_size = disk[file_index].0;
+        for i in 0..file_index {
+            let free_block = disk[i].1;
+            let free_size = disk[i].0;
+
+            if matches!(free_block, Block::Free) && free_size >= file_size {
+                let left_free_space = disk[file_index - 1].0;
+                let right_free_space = disk[file_index + 1].0;
+
+                disk[file_index - 1] =
+                    (left_free_space + file_size + right_free_space, Block::Free);
+                disk.remove(file_index);
+                disk.remove(file_index);
+
+                disk.insert(i, (file_size, file_block));
+                disk.insert(i, (0, Block::Free));
+                disk[i + 2] = (free_size - file_size, Block::Free);
+
+                break;
+            }
+        }
+    }
+
+    let mut result = 0;
+    let mut i = 0;
+    for (size, block) in disk {
+        if let Block::File(id) = block {
+            for x in i..i + size {
+                result += x * id;
+            }
+        }
+        i += size;
+    }
+
+    // 6239712239037 too low
+    Some(result as u64)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(1928));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(2858));
+    }
+}