Day 6

Cargo.toml

@@ -22,3 +22,7 @@ path = "src/day4.rs"
 [[bin]]
 name = "day5"
 path = "src/day5.rs"
+
+[[bin]]
+name = "day6"
+path = "src/day6.rs"

inputs/day6.txt

@@ -0,0 +1 @@
+5,1,5,3,2,2,3,1,1,4,2,4,1,2,1,4,1,1,5,3,5,1,5,3,1,2,4,4,1,1,3,1,1,3,1,1,5,1,5,4,5,4,5,1,3,2,4,3,5,3,5,4,3,1,4,3,1,1,1,4,5,1,1,1,2,1,2,1,1,4,1,4,1,1,3,3,2,2,4,2,1,1,5,3,1,3,1,1,4,3,3,3,1,5,2,3,1,3,1,5,2,2,1,2,1,1,1,3,4,1,1,1,5,4,1,1,1,4,4,2,1,5,4,3,1,2,5,1,1,1,1,2,1,5,5,1,1,1,1,3,1,4,1,3,1,5,1,1,1,5,5,1,4,5,4,5,4,3,3,1,3,1,1,5,5,5,5,1,2,5,4,1,1,1,2,2,1,3,1,1,2,4,2,2,2,1,1,2,2,1,5,2,1,1,2,1,3,1,3,2,2,4,3,1,2,4,5,2,1,4,5,4,2,1,1,1,5,4,1,1,4,1,4,3,1,2,5,2,4,1,1,5,1,5,4,1,1,4,1,1,5,5,1,5,4,2,5,2,5,4,1,1,4,1,2,4,1,2,2,2,1,1,1,5,5,1,2,5,1,3,4,1,1,1,1,5,3,4,1,1,2,1,1,3,5,5,2,3,5,1,1,1,5,4,3,4,2,2,1,3

src/day6.rs

@@ -0,0 +1,55 @@
+fn main() {
+    const INPUT: &'static str = include_str!("../inputs/day6.txt");
+    let fishes: Vec<usize> = INPUT
+        .strip_suffix('\n')
+        .unwrap()
+        .split(',')
+        .map(|timer| timer.parse::<usize>().unwrap())
+        .collect();
+    println!("solution {}", solve(fishes.clone(), 80));
+    println!("solution {}", solve(fishes.clone(), 256));
+}
+
+const BIRTH_RATE: usize = 7;
+const MATURITY: usize = 9;
+
+fn solve(fishes: Vec<usize>, days: usize) -> u64 {
+    let mut timers = [0u64; BIRTH_RATE];
+    let mut new_timers = [0u64; MATURITY];
+
+    for fish in fishes {
+        timers[fish] += 1;
+    }
+
+    for day in 0..days {
+        let spawns = timers[day % BIRTH_RATE];
+        let adults = new_timers[day % MATURITY];
+        new_timers[day % MATURITY] += spawns;
+        timers[day % BIRTH_RATE] += adults;
+    }
+    timers.iter().sum::<u64>() + new_timers.iter().sum::<u64>()
+}
+
+#[test]
+fn test_initial_state() {
+    let fishes = vec![3, 4, 3, 1, 2];
+    assert_eq!(solve(fishes, 0), 5);
+}
+
+#[test]
+fn test_18days() {
+    let fishes = vec![3, 4, 3, 1, 2];
+    assert_eq!(solve(fishes, 18), 26);
+}
+
+#[test]
+fn test_80days() {
+    let fishes = vec![3, 4, 3, 1, 2];
+    assert_eq!(solve(fishes, 80), 5934);
+}
+
+#[test]
+fn test_256days() {
+    let fishes = vec![3, 4, 3, 1, 2];
+    assert_eq!(solve(fishes, 256), 26984457539);
+}