solution: day 18

src/days.rs

@@ -15,7 +15,7 @@ pub mod d14;
 pub mod d15;
 pub mod d16;
 pub mod d17;
-// pub mod d18;
+pub mod d18;
 // pub mod d19;
 // pub mod d20;
 // pub mod d21;

src/days/d18.rs

@@ -0,0 +1,64 @@
+use crate::prelude::*;
+
+pub type I = &'static str;
+pub type O = usize;
+
+// @TODO: try bit mast approach
+fn _solve (data: I, rows: usize) -> O {
+    let w = data.len();
+    let mut v = vec![data.to_owned()];
+
+    while v.len() < rows {
+        let mut v2 = String::new();
+        let prev = &v[v.len() - 1].chars().collect_vec();
+
+        for i in 0..w {
+            let next = match (
+                i.checked_sub(1).map(|i| prev.get(i)).flatten().unwrap_or(&'.'),
+                prev.get(i).unwrap_or(&'.'),
+                prev.get(i+1).unwrap_or(&'.')
+            ) {
+                ('^', '^', '.') | ('.', '^', '^') | ('^', '.', '.') | ('.', '.', '^') => '^',
+                _ => '.'
+            };
+
+            v2.push(next);
+        }
+        v.push(v2);
+    }
+    v.concat().chars().filter(|&c| c == '.').count()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        inc!(18).trim()
+    }
+
+    #[test]
+    fn example () {
+        let data = ".^^.^.^^^^";
+        let ans = _solve(data, 10);
+        assert_eq!(ans, 38);
+
+        let data = "..^^.";
+        let ans = _solve(data, 3);
+        assert_eq!(ans, 6);
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _solve(data, 40);
+        assert_eq!(ans, 1982)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _solve(data, 400_000);
+        assert_eq!(ans, 20005203)
+    }
+}