feat: day 11 p1

src/bin/11.rs

@@ -0,0 +1,58 @@
+advent_of_code::solution!(11);
+
+use std::iter::successors;
+
+fn update_stones(stones: &Vec<u64>) -> Vec<u64> {
+    stones.into_iter().flat_map(|st|
+        match (st, st.checked_ilog10().unwrap_or(0) + 1) {
+            (0, _) => vec![1],
+            (n, digits) if digits % 2 == 0 && digits > 0 => {
+                let div = 10u64.pow(digits / 2);
+                vec![
+                    n / div,
+                    n % div,
+                ]
+            },
+            _ => vec![st * 2024],
+        }
+    ).collect()
+}
+
+fn parse_input(input: &str) -> Result<Vec<u64>, std::num::ParseIntError> {
+    input.split_whitespace().map(|c| c.parse::<u64>()).collect()
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let stones = parse_input(input).ok()?;
+    successors(Some(stones), |st| Some(update_stones(st)))
+        .nth(25)
+        .unwrap()
+        .len()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let stones = parse_input(input).ok()?;
+    successors(Some(stones), |st| Some(update_stones(st)))
+        .nth(75)
+        .unwrap()
+        .len()
+        .into()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one("125 17");
+        assert_eq!(result, Some(55312));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}