solve: day11

Author: tom-anders

Cargo.toml

@@ -2,7 +2,7 @@
 resolver = "2"
 members = [
     "utils",
-    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8", "day9", "day10",
+    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8", "day9", "day10", "day11",
 ]
 
 [workspace.dependencies]

day11/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "day11"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+aoc_derive.path = '../aoc_derive'
+utils.path = '../utils'
+derive_more.workspace = true
+itertools.workspace = true
+lazy-regex.workspace = true
+parse-display.workspace = true
+rayon.workspace = true
+regex.workspace = true
+num.workspace = true
+
+[dev-dependencies]
+pretty_assertions.workspace = true

day11/src/main.rs

@@ -0,0 +1,50 @@
+use std::collections::HashMap;
+
+use aoc_derive::aoc_main;
+use itertools::Itertools;
+use utils::*;
+
+fn iterate(stone: usize, depth: usize, cache: &mut HashMap<(usize, usize), usize>) -> usize {
+    if depth == 0 {
+        return 1;
+    }
+
+    if let Some(cached) = cache.get(&(stone, depth)) {
+        *cached
+    } else {
+        let count = if stone == 0 {
+            iterate(1, depth - 1, cache)
+        } else {
+            let s = stone.to_string();
+            if s.len() % 2 == 0 {
+                iterate(s[s.len() / 2..].parse().unwrap(), depth - 1, cache)
+                    + iterate(s[..s.len() / 2].parse().unwrap(), depth - 1, cache)
+            } else {
+                iterate(stone * 2024, depth - 1, cache)
+            }
+        };
+        cache.insert((stone, depth), count);
+        count
+    }
+}
+
+#[aoc_main]
+fn solve(input: Input) -> impl Into<Solution> {
+    let stones = input.as_str().split(' ').flat_map(str::parse).collect_vec();
+
+    let mut cache = HashMap::new();
+    (
+        stones.iter().map(|stone| iterate(*stone, 25, &mut cache)).sum_usize(),
+        stones.iter().map(|stone| iterate(*stone, 75, &mut cache)).sum_usize(),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_examples() {
+        use utils::assert_example;
+        assert_example!("125 17", 55312);
+    }
+}