1 files changed, 59 insertions, 0 deletions
diff --git a/2023/day08.rs b/2023/day08.rs
new file mode 100644
index 0000000..510ddba
--- /dev/null
+++ b/2023/day08.rs
@@ -0,0 +1,59 @@
+use num::integer::lcm;
+use std::collections::HashMap;
+use std::fs::File;
+use std::io::Read;
+
+fn main() {
+    // let filename = "in/day08.ref";
+    let filename = "in/day08.pzl";
+
+    let mut f = File::open(filename).expect("cannot open file");
+    let mut content = String::new();
+    f.read_to_string(&mut content).expect("cannot read file");
+    let mut lines = content.trim_end().split("\n\n");
+
+    let ops: Vec<char> = lines.next().unwrap().chars().collect();
+
+    let mut tree: HashMap<&str, (&str, &str)> = HashMap::new();
+    for line in lines.next().unwrap().split('\n') {
+        let (first, rest) = line.split_once(" = ").unwrap();
+        let (left, right) = rest.split_once(", ").unwrap();
+        let left = &left[1..];
+        let right = &right[..3];
+        tree.insert(first, (left, right));
+    }
+
+    let traverse_tree_until = |start: &str, f: fn(&str) -> bool| {
+        let mut loc = start;
+        let mut steps: usize = 0;
+        loop {
+            let (left, right) = tree.get(loc).unwrap();
+            let op = ops[steps % ops.len()];
+
+            if op == 'L' {
+                loc = left;
+            } else {
+                loc = right;
+            }
+            if f(&loc) {
+                break;
+            }
+            steps += 1;
+        }
+        (steps + 1) as u64
+    };
+
+    let res1 = traverse_tree_until("AAA", |x| x == "ZZZ");
+
+    let locs = tree.keys().filter(|x| &x[2..3] == "A").collect::<Vec<_>>();
+    let mut stps: Vec<u64> = Vec::new();
+    for i in 0..locs.len() {
+        stps.push(traverse_tree_until(locs[i], |x| x.ends_with("Z")));
+    }
+    let res2 = stps.iter().fold(1, |x, y| lcm(x, *y));
+
+    println!("res1: {}", res1);
+    println!("res2: {}", res2);
+    assert_eq!(res1, 14257);
+    assert_eq!(res2, 16187743689077);
+}