1 files changed, 79 insertions, 0 deletions
diff --git a/src/bin/2020/day2.rs b/src/bin/2020/day2.rs
new file mode 100644
index 0000000..9d25860
--- /dev/null
+++ b/src/bin/2020/day2.rs
@@ -0,0 +1,79 @@
+use advent_of_code::prelude::*;
+
+pub struct Line {
+    c: char,
+    n1: usize,
+    n2: usize,
+    password: String,
+}
+
+impl std::str::FromStr for Line {
+    type Err = anyhow::Error;
+
+    fn from_str(line: &str) -> Result<Self, Self::Err> {
+        let captures =
+            regex_captures!(r"^([0-9]+)-([0-9]+) (.): (.*)$", line)
+                .context("line failed to match regex")?;
+        let c = captures
+            .get(3)
+            .unwrap()
+            .as_str()
+            .parse()
+            .context("invalid policy char")?;
+        let n1 = captures
+            .get(1)
+            .unwrap()
+            .as_str()
+            .parse()
+            .context("invalid policy lower bound")?;
+        let n2 = captures
+            .get(2)
+            .unwrap()
+            .as_str()
+            .parse()
+            .context("invalid policy upper bound")?;
+        let password = captures.get(4).unwrap().as_str().to_string();
+        Ok(Self {
+            c,
+            n1,
+            n2,
+            password,
+        })
+    }
+}
+
+impl Line {
+    fn valid_part_1(&self) -> bool {
+        let count = self.password.chars().filter(|c| *c == self.c).count();
+        count >= self.n1 && count <= self.n2
+    }
+
+    fn valid_part_2(&self) -> bool {
+        (self.password.chars().nth(self.n1 - 1) == Some(self.c))
+            ^ (self.password.chars().nth(self.n2 - 1) == Some(self.c))
+    }
+}
+
+pub fn parse(fh: File) -> Result<impl Iterator<Item = Line>> {
+    Ok(parse::lines(fh))
+}
+
+pub fn part1(lines: impl Iterator<Item = Line>) -> Result<usize> {
+    Ok(lines.filter(|l| l.valid_part_1()).count())
+}
+
+pub fn part2(lines: impl Iterator<Item = Line>) -> Result<usize> {
+    Ok(lines.filter(|l| l.valid_part_2()).count())
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        part1(parse(parse::data(2020, 2).unwrap()).unwrap()).unwrap(),
+        638
+    );
+    assert_eq!(
+        part2(parse(parse::data(2020, 2).unwrap()).unwrap()).unwrap(),
+        699
+    );
+}