Day 11

Author: UnderscoreTud

README.md

@@ -35,9 +35,10 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 7](./src/bin/07.rs) | `80.3µs` | `113.7µs` |
 | [Day 8](./src/bin/08.rs) | `10.2µs` | `12.4µs` |
 | [Day 9](./src/bin/09.rs) | `2.9ms` | `49.1ms` |
-| [Day 10](./src/bin/10.rs) | `95.6µs` | `96.8µs` |
+| [Day 10](./src/bin/10.rs) | `96.9µs` | `97.3µs` |
+| [Day 11](./src/bin/11.rs) | `216.1µs` | `10.9ms` |
 
-**Total: 176.11ms**
+**Total: 187.23ms**
 <!--- benchmarking table --->
 
 ---

data/examples/11.txt

@@ -0,0 +1 @@
+125 17

src/bin/11.rs

@@ -0,0 +1,65 @@
+use itertools::Itertools;
+use std::collections::HashMap;
+
+advent_of_code::solution!(11);
+
+fn blink(stone: u64, iterations_left: usize, memo: &mut HashMap<(u64, usize), u64>) -> u64 {
+    if iterations_left == 0 {
+        return 1;
+    }
+    if let Some(cached_value) = memo.get(&(stone, iterations_left)) {
+        return *cached_value;
+    }
+
+    let (first_half, second_half) = blink_stone(stone);
+    let mut sum = blink(first_half, iterations_left - 1, memo);
+    if let Some(second_half) = second_half { sum += blink(second_half, iterations_left - 1, memo); }
+
+    memo.insert((stone, iterations_left), sum);
+
+    sum
+}
+
+fn blink_stone(stone: u64) -> (u64, Option<u64>) {
+    if stone == 0 {
+        return (1, None);
+    }
+
+    let digits = stone.ilog10() + 1;
+    if digits % 2 != 0 {
+        return (stone * 2024, None)
+    }
+    let divisor = 10u64.pow(digits / 2);
+    let first_half = stone / divisor;
+    let second_half = stone % divisor;
+    (first_half, Some(second_half))
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let stones = input.split_ascii_whitespace().map(|number| number.parse::<u64>().unwrap()).collect_vec();
+    let mut memo = HashMap::new();
+    Some(stones.iter().map(|stone| blink(*stone, 25, &mut memo)).sum())
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let stones = input.split_ascii_whitespace().map(|number| number.parse::<u64>().unwrap()).collect_vec();
+    let mut memo = HashMap::new();
+    Some(stones.iter().map(|stone| blink(*stone, 75, &mut memo)).sum())
+}
+
+#[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(55312));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(65601038650482));
+    }
+}