day 8

day8/src/main.rs

@@ -0,0 +1,45 @@
+use std::fs::read_to_string;
+use std::collections::HashMap;
+use num::integer::lcm;
+
+fn get_steps_to(directions: &str, nodes: &HashMap<&str, (&str, &str)>,
+                start: &str, stop: fn(&str) -> bool) -> u64 {
+    let mut current_node = start;
+    let mut counter: u64 = 0;
+    'outer: loop {
+        for c in directions.bytes() {
+            let (left, right) = nodes[current_node];
+            match c {
+                b'L' => current_node = left,
+                b'R' => current_node = right,
+                _ => {}
+            }
+            counter += 1;
+            if stop(current_node) {
+                break 'outer;
+            }
+        }
+    }
+    counter
+}
+
+fn main() {
+    let lines_str = read_to_string("input.txt").unwrap();
+    let mut lines_iter = lines_str.lines();
+    let directions = lines_iter.next().unwrap();
+    lines_iter.next();
+    let mut nodes: HashMap<&str, (&str, &str)> = HashMap::new();
+    for line in lines_iter {
+        let mut ids = line.split([' ', '(', ')', '=', ',']).filter(|&str| !str.is_empty());
+        nodes.insert(ids.next().unwrap(), (ids.next().unwrap(), ids.next().unwrap()));
+    }
+    let counter1 = get_steps_to(directions, &nodes, "AAA", |str| str == "ZZZ");
+    let counter2 = nodes.iter()
+        .filter_map(|(&id, _)|
+            Some(id).filter(|&id| id.as_bytes()[2 as usize] == b'A'))
+        .map(|node| get_steps_to(
+            directions, &nodes, node, |str| str.as_bytes()[2 as usize] == b'Z'))
+        .fold(1 as u64, |acc, counter| lcm(acc, counter));
+    println!("{}", counter1);
+    println!("{}", counter2);
+}