solution: day 17

src/days.rs

@@ -14,7 +14,7 @@ pub mod d13;
 pub mod d14;
 pub mod d15;
 pub mod d16;
-// pub mod d17;
+pub mod d17;
 // pub mod d18;
 // pub mod d19;
 // pub mod d20;

src/days/d17.rs

@@ -0,0 +1,94 @@
+#![allow(non_upper_case_globals)]
+#![allow(unused_imports)]
+
+use md5::Digest;
+
+use crate::prelude::*;
+
+pub type I = &'static str;
+pub type O = String;
+pub type O2 = usize;
+
+const _cand: [(isize, isize, char); 4] = [(-1, 0, 'U'), (1, 0, 'D'), (0, -1, 'L'), (0, 1, 'R')];
+
+fn _open_doors ((y, x): (usize, usize), digest: Digest) -> Vec<(usize, usize, char)> {
+    let repr = format!("{:x}", digest);
+    let access: [char; 4] = repr.chars().take(4).collect_vec().try_into().unwrap();
+
+    _cand.iter()
+        .enumerate()
+        .filter_map(|(i, &(dy, dx, n))| match (y.checked_add_signed(dy), x.checked_add_signed(dx)) {
+            (Some(y), Some(x)) => if y <= 3 && x <= 3 { Some((y, x, n, i)) } else { None },
+            _ => None
+        })
+        .filter(|(_, _, _, idx)| ('b'..='f').contains(&access[*idx]))
+        .map(|(a, b, c, _)| (a, b, c))
+        .collect()
+}
+
+fn _digest (pass: &'static str, i: &str) -> Digest {
+    let full = format!("{pass}{i}");
+    md5::compute(full)
+}
+
+fn _dfs (cur: (usize, usize), path: &mut String, pass: &'static str) -> bool {
+    if cur == (3, 3) { return true; } else {
+        let digest = _digest(pass, &path);
+        let doors = _open_doors(cur, digest);
+        for (ny, nx, p) in doors {
+            path.push(p);
+            if _dfs((ny, nx), path, pass) {
+                return true;
+            } else {
+                path.pop();
+            }
+        }
+        return false;
+    }
+}
+
+fn _dfs_max (cur: (usize, usize), path: &mut String, pass: &'static str, max: &mut usize) {
+    if cur == (3, 3) {
+        *max = (*max).max(path.len());
+    } else {
+        let digest = _digest(pass, &path);
+        let doors = _open_doors(cur, digest);
+        for (ny, nx, p) in doors {
+            path.push(p);
+            _dfs_max((ny, nx), path, pass, max);
+            path.pop();
+        }
+    }
+}
+
+fn _silver (data: I) -> O {
+    let mut path = String::new();
+    _dfs((0, 0), &mut path, data);
+    path
+}
+
+fn _gold (data: I) -> O2 {
+    let mut path = String::new();
+    let mut max = 0;
+    _dfs_max((0, 0), &mut path, data, &mut max);
+    max
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    const pass: &'static str = "edjrjqaa";
+
+    #[test]
+    fn silver () {
+        let ans = _silver(pass);
+        assert_eq!(ans, s!("DUDRDLRRRD"))
+    }
+
+    #[test]
+    fn gold () {
+        let ans = _gold(pass);
+        assert_eq!(ans, 502)
+    }
+}