1 files changed, 81 insertions, 0 deletions
diff --git a/src/bin/day11.rs b/src/bin/day11.rs
new file mode 100644
index 0000000..fe8cd2e
--- /dev/null
+++ b/src/bin/day11.rs
@@ -0,0 +1,81 @@
+static DAY: u8 = 11;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", blink_stones(&input[0]));
+    println!("{DAY}b: {}", 0);
+}
+
+enum Stone {
+    Number(u64),
+    Split(Box<Stone>,Box<Stone>),
+}
+
+impl Stone {
+
+    fn blink_number(number: u64) -> Stone {
+        /* rule 1 */
+        if number == 0 {
+            return Stone::Number(1);
+        }
+
+        /* rule 2 */
+        let number_str = number.to_string();
+        if number_str.len() % 2 == 0 {
+            let left = number_str.chars().take(number_str.len() / 2).collect::<String>();
+            let right = number_str.chars().skip(number_str.len() / 2).collect::<String>();
+
+            let left = left.parse::<u64>().unwrap();
+            let right = right.parse::<u64>().unwrap();
+            return Stone::Split(Box::new(Stone::Number(left)), Box::new(Stone::Number(right)));
+        }
+
+        /* rule 3 */
+        Stone::Number(2024 * number)
+    }
+
+    fn blink_stone(stone: &Stone) -> Stone {
+        match stone {
+            Stone::Number(number) => Self::blink_number(*number),
+            Stone::Split(left, right) => Stone::Split(Box::new(Self::blink_stone(left)), Box::new(Self::blink_stone(right))),
+        }
+    }
+
+    fn blink(&mut self) {
+        *self = Self::blink_stone(self);
+    }
+
+    fn count(&self) -> usize {
+        match self {
+            Stone::Number(_) => 1,
+            Stone::Split(left, right) => left.count() + right.count(),
+        }
+    }
+}
+
+fn blink_stones(input: &str) -> usize {
+    let mut stones = Vec::new();
+    for val in input.split(" ") {
+        let number = val.parse::<u64>().unwrap();
+        stones.push(Stone::Number(number));
+    }
+    for _ in 0..25 {
+        for stone in stones.iter_mut() {
+            stone.blink();
+        }
+    }
+    stones.iter()
+          .map(|stone| stone.count())
+          .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = "125 17";
+        assert_eq!(blink_stones(input), 55312);
+    }
+}