day11: part 2 solution

11/Cargo.lock

@@ -0,0 +1,25 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day11"
+version = "0.1.0"
+dependencies = [
+ "itertools",
+]
+
+[[package]]
+name = "either"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60b1af1c220855b6ceac025d3f6ecdd2b7c4894bfe9cd9bda4fbb4bc7c0d4cf0"
+
+[[package]]
+name = "itertools"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "413ee7dfc52ee1a4949ceeb7dbc8a33f2d6c088194d9f922fb8318faf1f01186"
+dependencies = [
+ "either",
+]

11/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "day11"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+itertools = "0.13.0"

11/src/main.rs

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+use std::collections::HashMap;
+use std::fs::File;
+use std::io::{BufRead, BufReader, Lines};
+use std::time::{Duration, Instant};
+
+use itertools::Itertools;
+
+// BOILERPLATE
+type InputIter = Lines<BufReader<File>>;
+
+pub fn get_input() -> InputIter {
+    let f = File::open("input").unwrap();
+    let br = BufReader::new(f);
+    br.lines()
+}
+
+fn duration_format(duration: Duration) -> String {
+    match duration.as_secs_f64() {
+        x if x > 1.0 => format!("{:.3}s", x),
+        x if x > 0.010 => format!("{:.3}ms", x * 1e3),
+        x => format!("{:.3}us", x * 1e6),
+    }
+}
+
+fn main() {
+    let input = get_input();
+    let start = Instant::now();
+    let ans1 = problem1(input);
+    let duration1 = start.elapsed();
+    println!("Problem 1 solution: {} [{}]", ans1, duration_format(duration1));
+
+    let input = get_input();
+    let start = Instant::now();
+    let ans2 = problem2(input);
+    let duration2 = start.elapsed();
+    println!("Problem 2 solution: {} [{}]", ans2, duration_format(duration2));
+    println!("Total duration: {}", duration_format(duration1 + duration2));
+}
+
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+struct Stone {
+    value: u64,
+}
+
+impl Stone {
+    fn blink_once(self) -> Vec<Stone> {
+        let n_digits = if self.value == 0 { 1 } else { self.value.ilog10() + 1 };
+        if self.value == 0 {
+            vec![Stone { value: 1 }]
+        } else if n_digits % 2 == 0 {
+            let parts = (
+                self.value / 10u64.pow(n_digits / 2),
+                self.value % 10u64.pow(n_digits / 2),
+            );
+            vec![Stone { value: parts.0 }, Stone { value: parts.1 }]
+        } else {
+            vec![Stone {
+                value: self.value * 2024,
+            }]
+        }
+    }
+    fn blink(self, times: usize) -> Vec<Stone> {
+        let mut stones = vec![self];
+        for _ in 0..times {
+            stones = stones.iter().flat_map(|stone| stone.blink_once()).collect();
+        }
+        stones
+    }
+}
+// PROBLEM 1 solution
+
+fn problem1<T: BufRead>(mut input: Lines<T>) -> u64 {
+    let stones = input
+        .next()
+        .unwrap()
+        .unwrap()
+        .split_ascii_whitespace()
+        .map(|v| Stone {
+            value: v.parse().unwrap(),
+        })
+        .collect_vec();
+    stones.iter().flat_map(|stone| stone.blink(25)).count() as u64
+}
+
+fn count_blinks(stone: Stone, blinks: u64, cache: &mut HashMap<(u64, Stone), u64>) -> u64 {
+    if cache.contains_key(&(blinks, stone)) {
+        return cache[&(blinks, stone)];
+    }
+    let stones = stone.blink_once();
+    let result = if blinks == 1 {
+        stones.len() as u64
+    } else {
+        stones.iter().map(|s| count_blinks(*s, blinks - 1, cache)).sum()
+    };
+    cache.insert((blinks, stone), result);
+    result
+}
+
+// PROBLEM 2 solution
+fn problem2<T: BufRead>(mut input: Lines<T>) -> u64 {
+    let stones = input
+        .next()
+        .unwrap()
+        .unwrap()
+        .split_ascii_whitespace()
+        .map(|v| Stone {
+            value: v.parse().unwrap(),
+        })
+        .collect_vec();
+    let mut cache = HashMap::new();
+    stones.iter().map(|s| count_blinks(*s, 75, &mut cache)).sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+    use std::io::Cursor;
+
+    const EXAMPLE: &str = &"125 17";
+
+    #[test]
+    fn problem1_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem1(c.lines()), 55312);
+    }
+
+    #[test]
+    fn problem2_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem2(c.lines()), 55312);
+    }
+}