2020: day02: part 2

aoc2020/src/day02.rs

@@ -71,10 +71,67 @@ impl FromStr for PassPolicy {
     }
 }
 
+#[derive(Debug)]
+struct PassPolicyNew {
+    pos1: usize,
+    pos2: usize,
+    letter: u8,
+    password: String,
+}
+
+impl PassPolicyNew {
+    fn new(pos1: usize, pos2: usize, letter: u8, password: String) -> Self {
+        Self {
+            pos1,
+            pos2,
+            letter,
+            password,
+        }
+    }
+
+    fn is_valid(&self) -> bool {
+        let bytes = self.password.as_bytes();
+        (bytes[self.pos1 - 1] == self.letter) ^ (bytes[self.pos2 - 1] == self.letter)
+    }
+}
+
+impl FromStr for PassPolicyNew {
+    type Err = aoc::Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        let s = s.trim_end();
+
+        let space = s
+            .find(' ')
+            .ok_or_else(|| err!("couldn't parse password policy: didn't find space"))?;
+        let dash = s
+            .find('-')
+            .ok_or_else(|| err!("couldn't parse password policy: didn't find dash"))?;
+
+        let pos1 = s[..dash]
+            .parse::<usize>()
+            .map_err(|e| err!("couldn't  parse position: {}", e))?;
+        let pos2 = s[(dash + 1)..space]
+            .parse::<usize>()
+            .map_err(|e| err!("couldn't parse position: {}", e))?;
+
+        let colon = s
+            .find(':')
+            .ok_or_else(|| err!("couldn't parse password policy: didn't find colon"))?;
+
+        let letter = s.as_bytes()[colon - 1];
+
+        let password = &s[(colon + 2)..];
+
+        Ok(Self::new(pos1, pos2, letter, password.to_string()))
+    }
+}
+
 pub fn run() -> Result<String> {
     let mut res = String::with_capacity(128);
 
     writeln!(res, "part 1: {}", part1(INPUT)?)?;
+    writeln!(res, "part 2: {}", part2(INPUT)?)?;
 
     Ok(res)
 }
@@ -88,22 +145,44 @@ fn part1(input: &str) -> Result<usize> {
     Ok(policies.iter().filter(|policy| policy.is_valid()).count())
 }
 
+fn part2(input: &str) -> Result<usize> {
+    let policies = input
+        .lines()
+        .map(|line| line.parse::<PassPolicyNew>().map_err(|e| err!("{}", e)))
+        .collect::<Result<Vec<PassPolicyNew>>>()?;
+
+    Ok(policies.iter().filter(|policy| policy.is_valid()).count())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    static PROVIDED: &'static str = "1-3 a: abcde
-1-3 b: cdefg
-2-9 c: ccccccccc
-";
+    static PROVIDED1: &'static str = "1-3 a: abcde";
+    static PROVIDED2: &'static str = "1-3 b: cdefg";
+    static PROVIDED3: &'static str = "2-9 c: ccccccccc";
 
     #[test]
     fn part1_provided() {
-        assert_eq!(part1(PROVIDED).unwrap(), 2);
+        assert!(PROVIDED1.parse::<PassPolicy>().unwrap().is_valid());
+        assert!(!PROVIDED2.parse::<PassPolicy>().unwrap().is_valid());
+        assert!(PROVIDED3.parse::<PassPolicy>().unwrap().is_valid());
     }
 
     #[test]
     fn part1_real() {
         assert_eq!(part1(INPUT).unwrap(), 556);
     }
+
+    #[test]
+    fn part2_provided() {
+        assert!(PROVIDED1.parse::<PassPolicyNew>().unwrap().is_valid());
+        assert!(!PROVIDED2.parse::<PassPolicyNew>().unwrap().is_valid());
+        assert!(!PROVIDED3.parse::<PassPolicyNew>().unwrap().is_valid());
+    }
+
+    #[test]
+    fn part2_real() {
+        assert_eq!(part2(INPUT).unwrap(), 605);
+    }
 }