wip: day8

2023/src/bin/day08.rs

@@ -7,7 +7,7 @@ use aoc2023::{boilerplate, common::*};
 const DAY: usize = 08;
 type Parsed<'a> = (Vec<Direction>, HashMap<&'a str, (&'a str, &'a str)>);
 
-#[derive(Debug, PartialEq, Copy, Clone)]
+#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
 enum Direction {
     Left,
     Right,
@@ -27,18 +27,30 @@ fn parse_input(raw: &str) -> Parsed {
     (directions, map)
 }
 
-fn part1((directions, map): &Parsed) -> usize {
+fn part1(parsed: &Parsed) -> usize {
+    steps_until(parsed, "AAA", "ZZZ")
+}
+
+fn steps_until((directions, map): &Parsed, start: &str, target: &str) -> usize {
+    let mut visited = HashMap::new();
     directions
         .iter()
+        .enumerate()
         .cycle()
-        .scan("AAA", |pos, dir| {
+        .enumerate()
+        .scan(start, |pos, (i, (j, dir))| {
             let next = match dir {
                 Direction::Left => map.get(pos)?.0,
                 Direction::Right => map.get(pos)?.1,
             };
-            if next == "ZZZ" {
+            if next.ends_with("Z") {
+                println!("Found ghost after {}", i + 1);
+            }
+            if pos == &next || next.ends_with(target) || visited.contains_key(&(next, j)) {
+                println!("Stopping at {pos} (next {next}) after {i} steps");
                 None
             } else {
+                visited.insert((next, j), i);
                 *pos = next;
                 Some(next)
             }
@@ -48,9 +60,24 @@ fn part1((directions, map): &Parsed) -> usize {
 }
 
 fn part2(parsed: &Parsed) -> usize {
+    for (start, _) in parsed.1.iter().filter(|(start, _)| start.ends_with("A")) {
+        println!("{}", steps_until(parsed, start, start));
+    }
     unimplemented!()
 }
 
+#[cfg(test)]
+const TEST_INPUT_P2: &str = "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)";
+
 boilerplate! {
     TEST_INPUT == "LLR
 
@@ -59,9 +86,9 @@ BBB = (AAA, ZZZ)
 ZZZ = (ZZZ, ZZZ)",
     tests: {
         part1: { TEST_INPUT => 6 },
-        part2: { TEST_INPUT => 0 },
+        part2: { TEST_INPUT_P2 => 6 },
     },
     bench1 == 12083,
-    bench2 == 0,
+    bench2 == 0, // 183359899573 too low
     bench_parse: |(v, m): &Parsed| { assert_eq!(m["AAA"], ("MJJ", "QBJ")); (v.len(), v[0]) } => (281, Direction::Left),
 }