Day 11

Author: prevostc

README.md

@@ -21,8 +21,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 8](./src/bin/08.rs) | `7.4µs` | `15.5µs` |
 | [Day 9](./src/bin/09.rs) | `149.0µs` | `6.5ms` |
 | [Day 10](./src/bin/10.rs) | `31.1µs` | `28.6µs` |
+| [Day 11](./src/bin/11.rs) | `104.4µs` | `1.8ms` |
 
-**Total: 12.71ms**
+**Total: 14.61ms**
 <!--- benchmarking table --->
 
 ---

data/examples/11.txt

@@ -0,0 +1 @@
+125 17

src/bin/11.rs

@@ -0,0 +1,100 @@
+use rustc_hash::FxHashMap;
+
+use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
+
+advent_of_code::solution!(11);
+
+type Stone = u64;
+type Step = u8;
+type MemoKey = (Step, Stone);
+type Memo = FxHashMap<MemoKey, u64>;
+
+fn blink_rec(memo: &mut Memo, stone: Stone, times: Step) -> u64 {
+    if times == 0 {
+        return 1;
+    }
+    if let Some(count) = memo.get(&(times, stone)) {
+        return *count;
+    }
+
+    let res = {
+        let mut digit_count = 0;
+        let mut temp = stone;
+        while temp > 0 {
+            digit_count += 1;
+            temp /= 10;
+        }
+
+        if stone == 0 {
+            blink_rec(memo, 1, times - 1)
+        } else if digit_count % 2 == 0 {
+            let divisor = 10_u64.pow(digit_count / 2);
+            blink_rec(memo, stone / divisor, times - 1)
+                + blink_rec(memo, stone % divisor, times - 1)
+        } else {
+            blink_rec(memo, stone * 2024, times - 1)
+        }
+    };
+
+    memo.insert((times, stone), res);
+    res
+}
+
+fn parse_input(input: &str) -> Vec<Stone> {
+    input
+        .split_whitespace()
+        .filter(|p| !p.is_empty())
+        .map(|s| s.parse::<u64>())
+        .filter(|r| r.is_ok())
+        .map(|r| r.unwrap())
+        .collect::<Vec<_>>()
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let times = 25;
+    let stones = parse_input(input);
+    let mut memo = FxHashMap::with_capacity_and_hasher(100000, Default::default());
+    let count = stones
+        .iter()
+        .map(|start_stone| blink_rec(&mut memo, *start_stone, times))
+        .sum::<u64>();
+
+    Some(count as u64)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let times = 75;
+    let stones = parse_input(input);
+    let count = stones
+        .par_iter()
+        .map(|start_stone| {
+            let mut memo = FxHashMap::with_capacity_and_hasher(100000, Default::default());
+            blink_rec(&mut memo, *start_stone, times)
+        })
+        .sum::<u64>();
+
+    Some(count as u64)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // #[test]
+    // fn test_part_one() {
+    //     let result = part_one("125");
+    //     assert_eq!(result, Some(55312));
+    // }
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(55312));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}