solution: day 11

src/bin/11.rs

@@ -0,0 +1,72 @@
+use std::mem::swap;
+
+use hashbrown::HashMap;
+use itertools::Itertools;
+
+fn blink(map: &HashMap<usize, usize>, nmap: &mut HashMap<usize, usize>) {
+    for (&k, &v) in map.iter() {
+        match k {
+            0 => *nmap.entry(1).or_default() += v,
+            x if (x.ilog10() + 1) % 2 == 0 => {
+                let xlen = x.ilog10() + 1;
+                let xhalf = 10_usize.pow(xlen / 2);
+
+                *nmap.entry(x / xhalf).or_default() += v;
+                *nmap.entry(x % xhalf).or_default() += v;
+            }
+            x => *nmap.entry(x * 2024).or_default() += v,
+        }
+    }
+}
+
+fn solve(input: &str, blinks: usize) -> usize {
+    let v = input
+        .split(" ")
+        .filter_map(|x| x.parse().ok())
+        .collect_vec();
+
+    let mut map = HashMap::<usize, usize>::new();
+
+    for vv in v {
+        *map.entry(vv).or_default() += 1;
+    }
+
+    let mut nmap = HashMap::<usize, usize>::new();
+
+    for _ in 0..blinks {
+        blink(&map, &mut nmap);
+        map.clear();
+        swap(&mut map, &mut nmap);
+    }
+
+    map.values().sum()
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    solve(input, 25).into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    solve(input, 75).into()
+}
+
+aoc::solution!(11);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 11)),
+            Some(55312)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 11)),
+            Some(65601038650482)
+        );
+    }
+}