Solved AOC 2024 day 11

2024/src/day11.rs

@@ -0,0 +1,96 @@
+use std::collections::HashMap;
+
+const INPUT: &str = include_str!("../../2024/input/day11.txt");
+
+pub(crate) fn part1() -> usize {
+    solve_part1(INPUT)
+}
+
+pub(crate) fn part2() -> usize {
+    solve_part2(INPUT)
+}
+
+fn solve_part1(input: &str) -> usize {
+    Stones::from(input).blink(25).count()
+}
+
+fn solve_part2(input: &str) -> usize {
+    Stones::from(input).blink(75).count()
+}
+
+type StoneNum = u64;
+type Count = usize;
+
+struct Stones {
+    stones: HashMap<StoneNum, Count>,
+}
+
+impl From<&str> for Stones {
+    fn from(input: &str) -> Self {
+        let stones = input
+            .trim()
+            .split_whitespace()
+            .map(|n| (n.parse().unwrap(), 1))
+            .collect();
+        Stones { stones }
+    }
+}
+
+impl Stones {
+    fn count(&self) -> Count {
+        self.stones.values().map(|count| count).sum()
+    }
+
+    fn blink(mut self, count: u8) -> Self {
+        for _ in 0..count {
+            let mut next_stones = HashMap::new();
+            for (stone, count) in self.stones.drain() {
+                let next = Stones::blink_single(stone);
+                *next_stones.entry(next[0]).or_insert(0) += count;
+                if next.len() == 2 {
+                    *next_stones.entry(next[1]).or_insert(0) += count;
+                }
+            }
+            self.stones = next_stones;
+        }
+        self
+    }
+
+    fn blink_single(stone: StoneNum) -> Vec<StoneNum> {
+        match stone {
+            0 => vec![1],
+            n if n.to_string().len() % 2 == 0 => {
+                let divisor = (10 as StoneNum).pow((n.to_string().len() / 2) as u32);
+                vec![n / divisor, n % divisor]
+            }
+            n => vec![n * 2024],
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EXAMPLE1: &str = "0 1 10 99 999";
+    const EXAMPLE2: &str = "125 17";
+
+    #[test]
+    fn test_part1_example1() {
+        assert_eq!(7, Stones::from(EXAMPLE1).blink(1).count());
+    }
+    #[test]
+    fn test_part1_example2() {
+        assert_eq!(55_312, Stones::from(EXAMPLE2).blink(25).count());
+    }
+
+    #[test]
+    fn test_part1() {
+        assert_eq!(194_557, solve_part1(INPUT));
+    }
+
+    #[test]
+    fn test_part2() {
+        assert_eq!(231_532_558_973_909, solve_part2(INPUT));
+    }
+}

2024/src/main.rs

@@ -10,6 +10,7 @@ mod day07;
 mod day08;
 mod day09;
 mod day10;
+mod day11;
 mod hash_tile_grid;
 mod tile_grid;
 mod vec_2d;
@@ -26,6 +27,7 @@ fn main() {
     print_result(8, day08::part1(), day08::part2());
     print_result(9, day09::part1(), day09::part2());
     print_result(10, day10::part1(), day10::part2());
+    print_result(11, day11::part1(), day11::part2());
 }
 
 fn print_result(day: i32, part1: impl Display, part2: impl Display) {