solution: day 9

src/bin/09.rs

@@ -0,0 +1,79 @@
+use itertools::Itertools;
+
+fn decompress(input: &str, recursive: bool) -> usize {
+    let mut stack = input
+        .chars()
+        .filter(|x| !x.is_whitespace())
+        .rev()
+        .collect_vec();
+
+    let mut drained = vec![];
+    let mut count = 0;
+
+    while let Some(c) = stack.pop() {
+        if c == '(' {
+            let mut n = 0;
+            let sublen = loop {
+                let l = stack.pop().unwrap();
+                if l == 'x' {
+                    break n;
+                }
+                n = n * 10 + l.to_digit(10).unwrap() as usize;
+            };
+
+            let mut n = 0;
+            let repeat = loop {
+                let l = stack.pop().unwrap();
+                if l == ')' {
+                    break n;
+                }
+                n = n * 10 + l.to_digit(10).unwrap() as usize;
+            };
+
+            drained.clear();
+
+            for _ in 0..sublen {
+                drained.push(stack.pop().unwrap());
+            }
+
+            if recursive {
+                for _ in 0..repeat {
+                    for d in drained.iter().copied().rev() {
+                        stack.push(d);
+                    }
+                }
+            } else {
+                count += drained.len() * repeat
+            }
+        } else {
+            count += 1
+        }
+    }
+
+    count
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    Some(decompress(input, false))
+}
+pub fn part_two(input: &str) -> Option<usize> {
+    Some(decompress(input, true))
+}
+fn main() {
+    let input = &aoc::read_file("inputs", 9);
+    aoc::solve!(part_one, part_two, input);
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        let input = aoc::read_file("examples", 9);
+        assert_eq!(part_one(&input), Some(238));
+    }
+    #[test]
+    fn test_part_two() {
+        let input = aoc::read_file("examples", 9);
+        assert_eq!(part_two(&input), Some(445));
+    }
+}

src/examples/09.txt

@@ -0,0 +1 @@
+(25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN