9th day

Author: majcn

data/examples/09.txt

@@ -0,0 +1 @@
+2333133121414131402

src/bin/09.rs

@@ -0,0 +1,115 @@
+advent_of_code::solution!(9);
+
+use advent_of_code::majcn::math::*;
+
+struct FileBlock {
+    id: usize,
+    size: usize,
+    position: usize,
+}
+
+struct FreeBlock {
+    size: usize,
+    position: usize,
+}
+
+fn parse_data(input: &str) -> (Vec<FileBlock>, Vec<FreeBlock>) {
+    let mut file_list = vec![];
+    let mut free_list = vec![];
+
+    let mut position = 0;
+
+    for (i, x) in input.bytes().enumerate() {
+        let size = (x - b'0') as usize;
+
+        if i % 2 == 0 {
+            file_list.push(FileBlock {
+                id: i / 2,
+                size,
+                position,
+            });
+        } else if x != 0 {
+            free_list.push(FreeBlock { size, position });
+        }
+
+        position += size;
+    }
+
+    (file_list, free_list)
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let (file_list, free_list) = parse_data(input);
+
+    let mut result = 0;
+
+    let mut free_index = 0;
+    let mut free_offset = 0;
+
+    for file in file_list.into_iter().rev() {
+        let mut file_free_swap = 0;
+        for file_offset in 0..file.size {
+            while free_list[free_index].size <= free_offset {
+                free_index += 1;
+                free_offset = 0;
+            }
+
+            let free_position = free_list[free_index].position + free_offset;
+            let position = if free_position < file.position {
+                free_offset += 1;
+                file_free_swap += 1;
+                free_position
+            } else {
+                file.position + file_offset - file_free_swap
+            };
+
+            result += file.id * position;
+        }
+    }
+
+    let result = result as u64;
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let (file_list, mut free_list) = parse_data(input);
+
+    let mut result = 0;
+
+    for mut file in file_list.into_iter().rev() {
+        let free_option = free_list
+            .iter_mut()
+            .take_while(|x| x.position < file.position)
+            .find(|x| x.size >= file.size);
+
+        if let Some(free) = free_option {
+            file.position = free.position;
+            free.position += file.size;
+            free.size -= file.size;
+        }
+
+        result += file.id * (file.size * file.position + (file.size - 1).sum_of_natural_numbers());
+    }
+
+    let result = result as u64;
+
+    Some(result)
+}
+
+#[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));
+    }
+}

src/majcn/math.rs

@@ -1,8 +1,20 @@
+pub trait SumOfNaturalNumbers<T> {
+    fn sum_of_natural_numbers(self) -> T;
+}
+
+impl SumOfNaturalNumbers<usize> for usize {
+    #[inline]
+    fn sum_of_natural_numbers(self) -> usize {
+        self * (self + 1) / 2
+    }
+}
+
 pub trait DigitCounter {
     fn count_digits(self) -> usize;
 }
 
 impl DigitCounter for u32 {
+    #[inline]
     fn count_digits(self) -> usize {
         match self {
             0..10 => 1,
@@ -19,6 +31,7 @@ impl DigitCounter for u32 {
 }
 
 impl DigitCounter for u64 {
+    #[inline]
     fn count_digits(self) -> usize {
         match self {
             0..10 => 1,