Day 6 in Rust

2021/rust/.gitignore

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+target/

2021/rust/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "rust"
+version = "0.1.0"

2021/rust/Cargo.toml

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+[package]
+name = "rust"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

2021/rust/src/bin/day6.rs

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+use std::io;
+
+fn main() {
+    let mut text = String::new();
+    io::stdin().read_line(&mut text).unwrap();
+    let mut data = vec![0u64; 9];
+    for c in text.strip_suffix("\n").unwrap().split(",") {
+        data[str::parse::<usize>(c).unwrap()] += 1;
+    }
+    for _ in 0..80 {
+        step(&mut data);
+    }
+    println!("{}", data.iter().sum::<u64>());
+    for _ in 80..256 {
+        step(&mut data);
+    }
+    println!("{}", data.iter().sum::<u64>());
+}
+
+fn step(data: &mut Vec<u64>) {
+    let d0 = data[0];
+    let mut prev = data[8];
+    for d in (0..=7).rev() {
+        let temp = data[d];
+        data[d] = prev;
+        prev = temp;
+    }
+    data[6] += d0;
+    data[8] = d0;
+}