From c8734354d4d7cc4fb822f426ef9f32a787420bb4 Mon Sep 17 00:00:00 2001
From: Federico Igne <git@federicoigne.com>
Date: Mon, 6 Dec 2021 14:33:31 +0000
Subject: Day 6

---
 day6/Cargo.toml          |  9 +++++++++
 day6/resources/input.txt |  1 +
 day6/src/main.rs         | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+)
 create mode 100644 day6/Cargo.toml
 create mode 100644 day6/resources/input.txt
 create mode 100644 day6/src/main.rs

(limited to 'day6')

diff --git a/day6/Cargo.toml b/day6/Cargo.toml
new file mode 100644
index 0000000..422ffef
--- /dev/null
+++ b/day6/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day6"
+version = "0.1.0"
+authors = ["Federico Igne <git@federicoigne.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day6/resources/input.txt b/day6/resources/input.txt
new file mode 100644
index 0000000..c35cc57
--- /dev/null
+++ b/day6/resources/input.txt
@@ -0,0 +1 @@
+5,1,1,5,4,2,1,2,1,2,2,1,1,1,4,2,2,4,1,1,1,1,1,4,1,1,1,1,1,5,3,1,4,1,1,1,1,1,4,1,5,1,1,1,4,1,2,2,3,1,5,1,1,5,1,1,5,4,1,1,1,4,3,1,1,1,3,1,5,5,1,1,1,1,5,3,2,1,2,3,1,5,1,1,4,1,1,2,1,5,1,1,1,1,5,4,5,1,3,1,3,3,5,5,1,3,1,5,3,1,1,4,2,3,3,1,2,4,1,1,1,1,1,1,1,2,1,1,4,1,3,2,5,2,1,1,1,4,2,1,1,1,4,2,4,1,1,1,1,4,1,3,5,5,1,2,1,3,1,1,4,1,1,1,1,2,1,1,4,2,3,1,1,1,1,1,1,1,4,5,1,1,3,1,1,2,1,1,1,5,1,1,1,1,1,3,2,1,2,4,5,1,5,4,1,1,3,1,1,5,5,1,3,1,1,1,1,4,4,2,1,2,1,1,5,1,1,4,5,1,1,1,1,1,1,1,1,1,1,3,1,1,1,1,1,4,2,1,1,1,2,5,1,4,1,1,1,4,1,1,5,4,4,3,1,1,4,5,1,1,3,5,3,1,2,5,3,4,1,3,5,4,1,3,1,5,1,4,1,1,4,2,1,1,1,3,2,1,1,4
\ No newline at end of file
diff --git a/day6/src/main.rs b/day6/src/main.rs
new file mode 100644
index 0000000..e3ef79c
--- /dev/null
+++ b/day6/src/main.rs
@@ -0,0 +1,48 @@
+use std::fs;
+use std::path::Path;
+
+/* AOC21 Day 6: https://adventofcode.com/2021/day/6 */
+fn main() {
+    let input = Path::new("resources").join("input.txt");
+    let content = fs::read_to_string(input).expect("Unable to read input file");
+    println!("Ex1: The number of lanternfishes is {}", evolution(parse_input(&content), 80));
+    println!("Ex2: The number of lanternfishes is {}", evolution(parse_input(&content), 256));
+}
+
+fn parse_input(s: &str) -> Vec<u64> {
+    let mut lfs = vec![0;9];
+    s.split(",").for_each(|n| lfs[n.parse::<usize>().expect("Malformed input")] += 1);
+    lfs
+}
+
+fn evolution(mut lfs: Vec<u64>, days: usize) -> u64 {
+    (1..days).for_each(|i| lfs[(i+7)%9] += lfs[i%9]);
+    lfs.iter().sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const LANTERNFISHES: &str = "3,4,3,1,2";
+
+    #[test]
+    fn input_parsing() {
+        assert_eq!(vec![0,1,1,2,1,0,0,0,0], parse_input("3,4,3,1,2"))
+    }
+
+    #[test]
+    fn evolution_18days() {
+        assert_eq!(26, evolution(parse_input(LANTERNFISHES), 18))
+    }
+
+    #[test]
+    fn evolution_80days() {
+        assert_eq!(5934, evolution(parse_input(LANTERNFISHES), 80))
+    }
+
+    #[test]
+    fn evolution_256days() {
+        assert_eq!(26984457539, evolution(parse_input(LANTERNFISHES), 256))
+    }
+}
-- 
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