Day 11 part 2

2024/rust/src/day11.rs

@@ -7,41 +7,47 @@ fn main() {
 }
 
 fn part1(input: &str) -> usize {
-    stone_blinks(input, 25)
+    stone_blinks_by_count(input, 25)
 }
 
-fn stone_blinks(input: &str, count: usize) -> usize {
-    let mut stones: Vec<usize> = input
+fn stone_blink(s: usize) -> Vec<usize> {
+    if s == 0 {
+        return vec![1];
+    }
+    let ss = s.to_string();
+    if ss.len() % 2 == 0 {
+        let mid = ss.len() / 2;
+        let (s1, s2) = (ss[0..mid].parse().unwrap(), ss[mid..].parse().unwrap());
+        return vec![s1, s2];
+    }
+    vec![s * 2024]
+}
+
+fn stone_blinks_by_count(input: &str, count: usize) -> usize {
+    let mut stones: HashMap<usize, usize> = input
         .trim()
         .split(" ")
-        .map(|s| s.parse().unwrap())
-        .collect();
-    let mut next_stones = vec![];
-    for blink in 0..count {
-        println!("{blink} {}", stones.len());
-        for (_i, s) in stones.iter().enumerate() {
-            // next_stones.push(*s)
-            if *s == 0 {
-                next_stones.push(1);
-                continue;
+        .map(|n| n.parse().unwrap())
+        .fold(HashMap::new(), |mut acc, n| {
+            *acc.entry(n).or_default() += 1;
+            acc
+        });
+    let mut next_stones: HashMap<usize, usize> = HashMap::new();
+    for _c in 0..count {
+        for (n, c) in &stones {
+            for nn in stone_blink(*n) {
+                *next_stones.entry(nn).or_default() += c;
             }
-            let ss = s.to_string();
-            if ss.len() % 2 == 0 {
-                let mid = ss.len() / 2;
-                let (s1, s2) = (ss[0..mid].parse().unwrap(), ss[mid..].parse().unwrap());
-                next_stones.push(s1);
-                next_stones.push(s2);
-                continue;
-            }
-            next_stones.push(s * 2024)
         }
-        stones = next_stones;
-        next_stones = vec![];
+        println!("afterblink\n{stones:?}\n{next_stones:?}");
+        (stones, next_stones) = (next_stones, HashMap::new());
     }
-    stones.len()
+    stones.into_values().sum()
 }
 
-fn part2(input: &str) -> usize {}
+fn part2(input: &str) -> usize {
+    stone_blinks_by_count(input, 75)
+}
 
 #[cfg(test)]
 mod tests {
@@ -51,6 +57,6 @@ mod tests {
     fn test() {
         let input = r#"125 17"#;
         assert_eq!(part1(input), 55312);
-        assert_eq!(part2(input), 0);
+        assert_eq!(part2(input), 65601038650482);
     }
 }

2024/rust/src/prelude.rs

@@ -10,6 +10,7 @@ pub use std::{
     iter::zip,
     num::{ParseFloatError, ParseIntError},
     str::FromStr,
+    sync::{Arc, LazyLock, Mutex},
 };
 
 pub type AnyResult<T> = std::result::Result<T, Box<dyn std::error::Error>>;