Added Day 6 Part 2

src/main.rs

@@ -15,26 +15,36 @@ fn parse_input(input: &'static str) -> Vec<u8> {
         .collect()
 }
 
-fn solution(fishes: Vec<u8>) -> u64 {
-    let mut day_stat = [0u64; 9];
-
+fn solution<const N: usize>(fishes: Vec<u8>) -> u64 {
+    let mut fish_stat = [0u64; 9];
     for fish in fishes {
-        day_stat[fish as usize] += 1;
+        fish_stat[fish as usize] += 1;
     }
 
-    for _ in 0..80 {
-        day_stat.rotate_left(1);
-
-        day_stat[6] += day_stat[8];
+    // Unrolled loop to improve performance
+    let blocks = N / 9;
+    for _ in 0..blocks {
+        fish_stat[7] += fish_stat[0];
+        fish_stat[8] += fish_stat[1];
+        fish_stat[0] += fish_stat[2];
+        fish_stat[1] += fish_stat[3];
+        fish_stat[2] += fish_stat[4];
+        fish_stat[3] += fish_stat[5];
+        fish_stat[4] += fish_stat[6];
+        fish_stat[5] += fish_stat[7];
+        fish_stat[6] += fish_stat[8];
+    }
+    for day in blocks * 9..N {
+        fish_stat[(day + 7) % 9] += fish_stat[day % 9];
     }
 
-    day_stat.into_iter().sum::<u64>()
+    fish_stat.into_iter().sum::<u64>()
 }
 
 fn main() {
     for input in INPUTS {
         let input = parse_input(input);
-        let result = solution(input);
+        let result = solution::<256>(input);
         println!("Result {}", result);
     }
 }
@@ -43,7 +53,7 @@ fn main() {
 fn solution_bench(b: &mut test::Bencher) {
     let input = parse_input(INPUTS[1]);
     b.iter(|| {
-        let result = solution(input.clone());
+        let result = solution::<256>(input.clone());
         test::black_box(result);
     })
 }