1 files changed, 33 insertions, 0 deletions

diff --git a/2021/day6/src/main.rs b/2021/day6/src/main.rs
new file mode 100644
index 0000000..378764e
--- /dev/null
+++ b/2021/day6/src/main.rs
@@ -0,0 +1,33 @@
+use std::env;
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+
+    if args.len() != 2 {
+        eprintln!("Usage: {} <filename>", args[0]);
+        std::process::exit(1);
+    }
+    let mut smart_lanternfish: [u64; 9] = [0; 9];
+
+    let foo: String = std::fs::read_to_string(&args[1]).unwrap().parse().unwrap();
+    let mut lanternfish: Vec<u8> = Vec::new();
+    lanternfish.extend(foo.trim().split(",").map(|x| x.parse::<u8>().unwrap()));
+
+    for initial_fish in &lanternfish {
+        smart_lanternfish[*initial_fish as usize] += 1;
+    }
+
+    // println!("{:?}", smart_lanternfish);
+    for _day in 0..256 {
+        smart_lanternfish.rotate_left(1);
+        smart_lanternfish[6] += smart_lanternfish[8];
+        // println!(
+        //     "After {day:>width$} days: {lanternfish:?}",
+        //     day = _day,
+        //     width = 2,
+        //     lanternfish = smart_lanternfish
+        // );
+    }
+
+    println!("{}", smart_lanternfish.iter().sum::<u64>());
+}