first two days

src/bin/01.rs

@@ -0,0 +1,56 @@
+advent_of_code::solution!(1);
+use regex::Regex;
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let dir_regex = Regex::new(r"(.)(\d+)").unwrap();
+
+    let (hits, _total) = dir_regex.captures_iter(input).fold((0u32, 50i32), |(hits, total), cap| {
+        let (_, [direction, value_str]) = cap.extract();
+        let value = value_str.parse::<i32>().unwrap();
+
+        let new_total = (total + 100 + if direction == "L" { -1i32 } else { 1 } * value) % 100;
+        let new_hits = if new_total == 0 { hits + 1 } else { hits };
+
+        // println!("{} + {} {} = {}", total, direction, value, new_total);
+
+        (new_hits, new_total)
+    });
+
+    Some(hits as u64)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+        let dir_regex = Regex::new(r"(.)(\d+)").unwrap();
+
+    let (hits, _total) = dir_regex.captures_iter(input).fold((0u32, 50i32), |(hits, total), cap| {
+        let (_, [direction, value_str]) = cap.extract();
+        let value: i32 = value_str.parse::<i32>().unwrap();
+
+        let new_total_unmod = total + if direction == "L" { -1i32 } else { 1 } * value;
+        let new_total = (new_total_unmod % 100 + 100) % 100;
+        let clicks_past_zero = (new_total_unmod / 100).abs() as u32 + if total != 0 && new_total_unmod <= 0 { 1 } else { 0 };
+
+        // println!("{} + {} {} = {} ({} total clicks, {} new)", total, direction, value, new_total, hits + clicks_past_zero, clicks_past_zero);
+
+        (hits + clicks_past_zero, new_total)
+    });
+
+    Some(hits as u64)
+}
+
+#[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(3));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(6));
+    }
+}