solution: day 13 (dfs)

src/days.rs

@@ -10,7 +10,7 @@ pub mod d9;
 pub mod d10;
 pub mod d11;
 pub mod d12;
-// pub mod d13;
+pub mod d13;
 // pub mod d14;
 // pub mod d15;
 // pub mod d16;

src/days/d13.rs

@@ -0,0 +1,74 @@
+#![allow(dead_code)]
+#![allow(non_upper_case_globals)]
+
+use crate::prelude::*;
+
+pub type O = usize;
+
+const INPUT: usize = 1358;
+
+
+fn is_wall (y: usize, x: usize) -> bool {
+    ((x*x + 3*x + 2*x*y + y + y*y) + INPUT).count_ones() % 2 != 0
+}
+
+fn next ((y, x, len): (usize, usize, usize)) -> Vec<(usize, usize, usize)> {
+    const cand: [(isize, isize); 4] = [(0, -1), (0, 1), (-1, 0), (1, 0)];
+
+    cand.into_iter().filter_map(|(dy, dx)| {
+        let ny = y.checked_add_signed(dy);
+        let nx = x.checked_add_signed(dx);
+
+        match (ny, nx) {
+            (Some(y), Some(x)) => if is_wall(y, x) { None } else { Some((y, x, len + 1)) },
+            _ => None
+        }
+    }).collect()
+}
+
+fn solve (visited: &mut M<(usize, usize), usize>) {
+    let mut stack = vec![(1, 1, 0)];
+    while !stack.is_empty() {
+        let c @ (y, x, len) = stack.pop().unwrap();
+
+        *visited.entry((y, x)).or_default() = len;
+        for n @ (ny, nx, nl) in next(c) {
+            if !visited.contains_key(&(ny, nx)) || visited.get(&(ny, nx)).is_some_and(|&old| old > nl) {
+                stack.push(n);
+            }
+        }
+    }
+}
+
+fn _silver () -> O {
+    let mut visited = M::new();
+    solve(&mut visited);
+    *visited.get(&(39, 31)).unwrap()
+}
+
+fn _gold () -> O {
+    let mut visited = M::new();
+    solve(&mut visited);
+    visited.values().filter(|&&e| e <= 50).count()
+}
+
+
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn silver () {
+        let ans = _silver();
+
+        assert_eq!(ans, 96)
+    }
+
+    #[test]
+    fn gold () {
+        let ans = _gold();
+
+        assert_eq!(ans, 141)
+    }
+}