Complete day 2

day-2/src/main.rs

@@ -0,0 +1,94 @@
+use std::fs;
+
+type PasswordPolicy = (usize, usize, char);
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("input")?;
+    println!("{}", count_valid_passwords(&input, &validate_password_new));
+    Ok(())
+}
+
+fn parse_password_line(line: &str) -> Result<(PasswordPolicy, &str), Box<dyn std::error::Error>> {
+    let mut sections = line.split(' ');
+    let range = sections
+        .next()
+        .ok_or("Password line too short")?
+        .split('-')
+        .map(|c| c.parse::<usize>())
+        .collect::<Result<Vec<usize>, _>>()?;
+
+    let character = sections
+        .next()
+        .ok_or("Password line too short")?
+        .chars()
+        .next()
+        .ok_or("Password line too short")?;
+    let password = sections.next().ok_or("Password line too short")?;
+
+    Ok(((range[0], range[1], character), password))
+}
+
+fn validate_password_old(policy: &PasswordPolicy, password: &str) -> bool {
+    let (start, end, character) = policy;
+
+    let occurrences = password.chars().filter(|c| c == character).count();
+    *start <= occurrences && occurrences <= *end
+}
+
+fn validate_password_new(policy: &PasswordPolicy, password: &str) -> bool {
+    let (position1, position2, character) = policy;
+    let position1_is_character = password
+        .chars()
+        .nth(position1 - 1)
+        .expect("Password too short")
+        == *character;
+    let position2_is_character = password
+        .chars()
+        .nth(position2 - 1)
+        .expect("Password too short")
+        == *character;
+
+    (position1_is_character || position2_is_character)
+        && (!position1_is_character || !position2_is_character)
+}
+
+fn count_valid_passwords(input: &str, validate: &dyn Fn(&PasswordPolicy, &str) -> bool) -> usize {
+    input
+        .lines()
+        .filter(|line| {
+            if let Ok((policy, password)) = parse_password_line(line) {
+                validate(&policy, password)
+            } else {
+                false
+            }
+        })
+        .count()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn test_simple() {
+        let example = indoc!(
+            "1-3 a: abcde
+             1-3 b: cdefg
+             2-9 c: ccccccccc"
+        );
+
+        assert_eq!(count_valid_passwords(&example, &validate_password_old), 2);
+    }
+
+    #[test]
+    fn test_simple2() {
+        let example = indoc!(
+            "1-3 a: abcde
+             1-3 b: cdefg
+             2-9 c: ccccccccc"
+        );
+
+        assert_eq!(count_valid_passwords(&example, &validate_password_new), 1);
+    }
+}