Day 11

src/day11.rs

@@ -0,0 +1,47 @@
+use std::collections::HashMap;
+
+const BLINKS: usize = 75;
+
+// (value, blinks_remaining)
+type Stone = (u64, usize);
+
+pub fn day11() {
+    let mut lut: HashMap<Stone, usize> = HashMap::new();
+    let count: usize = crate::input(11)
+        .split_whitespace()
+        .map(|s| s.parse().unwrap())
+        .map(|v| blink((v, BLINKS), &mut lut))
+        .sum();
+
+    println!("Total Stones: {}", count);
+}
+
+fn blink(stone: Stone, lut: &mut HashMap<Stone, usize>) -> usize {
+    if let Some(&count) = lut.get(&stone) {
+        return count;
+    }
+
+    let blinked = blink_single(stone);
+
+    let count = match stone.1 {
+        1 => blinked.len(),
+        _ => blinked.iter().map(|&s| blink(s, lut)).sum(),
+    };
+
+    lut.insert(stone, count);
+    count
+}
+
+fn blink_single((v, b): Stone) -> Vec<Stone> {
+    match v.to_string().as_str() {
+        "0" => vec![(1, b - 1)],
+        s if s.len() % 2 == 0 => {
+            let mid = s.len() / 2;
+            vec![
+                (s[..mid].parse().unwrap(), b - 1),
+                (s[mid..].parse().unwrap(), b - 1),
+            ]
+        }
+        _ => vec![(v * 2024, b - 1)],
+    }
+}

src/main.rs

@@ -16,10 +16,12 @@ mod day7;
 mod day8;
 #[allow(dead_code)]
 mod day9;
+#[allow(dead_code)]
 mod day10;
+mod day11;
 
 fn main() {
-    day10::day10();
+    day11::day11();
 }
 
 pub fn input(day: u8) -> String {