solution: day 9 (simulation approach)

src/days.rs

@@ -6,7 +6,7 @@ pub mod d5;
 pub mod d6;
 pub mod d7;
 pub mod d8;
-// pub mod d9;
+pub mod d9;
 // pub mod d10;
 // pub mod d11;
 // pub mod d12;

src/days/d9.rs

@@ -0,0 +1,108 @@
+use crate::prelude::*;
+
+pub type I = SS;
+pub type O = usize;
+
+fn _expand (mut data: impl Iterator<Item = char>) -> String {
+    let mut stack = String::new();
+
+    data.by_ref().take_while(|e| *e != '(').for_each(|c| stack.push(c));
+
+    let a = data.by_ref().take_while(|c| *c != ')').collect::<String>();
+    let Some((len, times)) = a.split_once('x') else { return stack };
+    let len = len.parse::<usize>().unwrap();
+    let mut taken = data.by_ref().take(len).filter(|e| !e.is_control() && !e.is_whitespace()).collect::<String>();
+
+    while let Some(p) = taken.find("(") {
+        let new = format!("{}{}", &taken[..p], _expand(taken[p..].chars()));
+        // println!("{:?} -> {:?}", taken, new);
+        taken = new;
+    }
+
+    let times = times.parse::<usize>().unwrap();
+    stack.push_str(&taken.repeat(times));
+    stack.push_str(&_expand(data));
+
+    stack
+}
+
+fn _silver (data: I) -> O {
+    let mut stack = String::new();
+    let mut cs = data.trim().chars();
+
+    loop {
+        let Some(cur) = cs.next() else { break; };
+
+        match cur {
+            '(' => {
+                let a = cs.by_ref().take_while(|c| *c != ')').collect::<String>();
+                let (len, times) = a.split_once('x').unwrap();
+                let len = len.parse::<usize>().unwrap();
+                let times = times.parse::<usize>().unwrap();
+                let taken = cs.by_ref().take(len).filter(|e| !e.is_control() && !e.is_whitespace()).collect::<String>();
+
+                stack.push_str(&taken.repeat(times));
+            },
+            e => stack.push(e),
+        }
+
+    }
+
+    stack.len()
+}
+
+fn _gold (data: I) -> O {
+    let stack = _expand(data.trim().chars());
+    stack.len()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        inc!(9)
+    }
+
+    #[test]
+    fn sample () {
+
+        let cases = [
+            ("ADVENT", 6),
+            ("X(8x2)(3x3)ABCY", 18),
+            ("A(1x5)BC", 7),
+            ("(3x3)XYZ", 9),
+            ("A(2x2)BCD(2x2)EFG", 11),
+            ("(6x1)(1x3)A", 6),
+        ];
+
+        for (i, o) in cases {
+            assert_eq!(_silver(i), o)
+        }
+
+        let cases_gold = [
+            ("X(8x2)(3x3)ABCY", 20),
+            ("(25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN", 445),
+        ];
+
+        for (i, o) in cases_gold {
+            assert_eq!(_gold(i), o)
+        }
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _silver(&data);
+
+        assert_eq!(ans, 74532)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _gold(&data);
+
+        assert_eq!(ans, 11558231665)
+    }
+}