Day 8

Cargo.lock

@@ -57,3 +57,11 @@ version = "0.1.0"
 [[package]]
 name = "d07t2"
 version = "0.1.0"
+
+[[package]]
+name = "d08t1"
+version = "0.1.0"
+
+[[package]]
+name = "d08t2"
+version = "0.1.0"

Cargo.toml

@@ -16,4 +16,6 @@ members = [
     "d06t2",
     "d07t1",
     "d07t2",
+    "d08t1",
+    "d08t2",
 ]

d08t1/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "d08t1"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

d08t1/demo_input.txt

@@ -0,0 +1,5 @@
+LLR
+
+AAA = (BBB, BBB)
+BBB = (AAA, ZZZ)
+ZZZ = (ZZZ, ZZZ)

d08t1/src/main.rs

@@ -0,0 +1,40 @@
+use std::{collections::HashMap, fs::read_to_string};
+
+fn main() {
+    let input = read_to_string("input.txt").unwrap();
+    println!("d08t1: {}", d08t1(&input));
+}
+
+#[must_use]
+pub fn d08t1(input: &str) -> usize {
+    let mut lines = input.lines();
+    let mut directions = lines.next().unwrap().chars().cycle();
+    let mut locations: HashMap<String, (String, String)> = HashMap::new();
+    for line in lines.skip(1) {
+        let (source, destination) = line.split_once(" = ").unwrap();
+        let destination = &destination.replace(['(', ')'], "");
+        let (left, right) = destination.split_once(", ").unwrap();
+        locations.insert(source.to_string(), (left.to_string(), right.to_string()));
+    }
+    let mut result = 0;
+    let mut current_position = "AAA";
+    while current_position != "ZZZ" {
+        result += 1;
+        current_position = if directions.next().unwrap() == 'L' {
+            &locations.get(current_position).unwrap().0
+        } else {
+            &locations.get(current_position).unwrap().1
+        };
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_d08t1() {
+        let input = include_str!("../demo_input.txt");
+        assert_eq!(d08t1(input), 6);
+    }
+}

d08t2/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "d08t2"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

d08t2/demo_input.txt

@@ -0,0 +1,10 @@
+LR
+
+11A = (11B, XXX)
+11B = (XXX, 11Z)
+11Z = (11B, XXX)
+22A = (22B, XXX)
+22B = (22C, 22C)
+22C = (22Z, 22Z)
+22Z = (22B, 22B)
+XXX = (XXX, XXX)

d08t2/src/main.rs

@@ -0,0 +1,65 @@
+use std::{collections::HashMap, fs::read_to_string};
+
+fn main() {
+    let input = read_to_string("input.txt").unwrap();
+    println!("d08t2: {}", d08t2(&input));
+}
+
+pub fn d08t2(input: &str) -> usize {
+    let mut lines = input.lines();
+    let directions = lines.next().unwrap().chars().cycle();
+    let mut locations: HashMap<String, (String, String)> = HashMap::new();
+    for line in lines.skip(1) {
+        let (source, destination) = line.split_once(" = ").unwrap();
+        let destination = &destination.replace(['(', ')'], "");
+        let (left, right) = destination.split_once(", ").unwrap();
+        locations.insert(source.to_string(), (left.to_string(), right.to_string()));
+    }
+    let keys = locations.keys();
+    keys.filter(|k| k.ends_with('A'))
+        .map(Clone::clone)
+        .map(|start| {
+            let mut dirs = directions.clone();
+            let mut res = 0;
+            let mut current_position = start.clone();
+            while !current_position.ends_with('Z') {
+                res += 1;
+                current_position = if dirs.next().unwrap() == 'L' {
+                    &locations.get(&current_position).unwrap().0
+                } else {
+                    &locations.get(&current_position).unwrap().1
+                }
+                .clone();
+            }
+            res
+        })
+        .reduce(lcm)
+        .unwrap()
+}
+
+fn lcm(first: usize, second: usize) -> usize {
+    first * second / gcd(first, second)
+}
+
+fn gcd(first: usize, second: usize) -> usize {
+    let mut max = first.max(second);
+    let mut min = first.min(second);
+    loop {
+        let res = max % min;
+        if res == 0 {
+            return min;
+        }
+        max = min;
+        min = res;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_d08t2() {
+        let input = include_str!("../demo_input.txt");
+        assert_eq!(d08t2(input), 6);
+    }
+}