solution: day 3

data/examples/03.txt

@@ -0,0 +1 @@
+xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))

src/bin/03.rs

@@ -0,0 +1,52 @@
+use regex::Regex;
+
+fn solve(input: &str, flip: bool) -> usize {
+    let r = Regex::new(r"mul\((\d+),(\d+)\)|do\(\)|don't\(\)").unwrap();
+
+    let mut enabled = true;
+    let mut res = 0;
+
+    for c in r.captures_iter(input) {
+        let full = c.get(0).unwrap().as_str();
+        match &full[..=2] {
+            "mul" => {
+                if enabled {
+                    let a: usize = c.get(1).unwrap().as_str().parse().unwrap();
+                    let b: usize = c.get(2).unwrap().as_str().parse().unwrap();
+                    res += a * b;
+                }
+            }
+            "do(" => enabled = true,
+            "don" => enabled = !flip,
+            _ => unreachable!(),
+        }
+    }
+
+    res
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    solve(input, false).into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    solve(input, true).into()
+}
+
+aoc::solution!(3);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 3)),
+            Some(161)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 3)), Some(48));
+    }
+}