feat: add day 3

src/bin/03.rs

@@ -0,0 +1,51 @@
+advent_of_code::solution!(3);
+
+use regex::Regex;
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let re = Regex::new(r"mul\((\d+),(\d+)\)").unwrap();
+    re.captures_iter(input)
+        .map(|c| match c.extract() {
+            (_, [a, b]) => a.parse::<u32>().unwrap() * b.parse::<u32>().unwrap()
+        })
+        .sum::<u32>()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let re = Regex::new(r"(?:(mul)\((\d+),(\d+)\))|(?:(do)(\()(\)))|(?:(don't)(\()(\)))").unwrap();
+    re.captures_iter(input)
+     .map(|c| match c.extract() {
+         (_, ["mul", a, b]) => (None, a.parse::<u32>().unwrap() * b.parse::<u32>().unwrap()),
+         (_, ["do", _, _]) => (Some(true), 0),
+         (_, ["don't", _, _]) => (Some(false), 0),
+         _ => panic!("invalid parsing"),
+     })
+     .fold((true, 0), |(flag, acc), (op_flag, op_res)|
+         match (flag, acc, op_flag, op_res) {
+             (_, acc, Some(new_flag), _) => (new_flag, acc),
+             (false, acc, None, _) => (false, acc),
+             (true, acc, None, new) => (true, acc + new),
+         }
+     )
+     .1
+     .into()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(161));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(48));
+    }
+}
+