Rust Day 2

rust/Cargo.toml

@@ -26,3 +26,7 @@ codegen-units = 1
 [[bin]]
 name = "day01"
 path = "src/day01/main.rs"
+
+[[bin]]
+name = "day02"
+path = "src/day02/main.rs"

rust/src/day02/main.rs

@@ -0,0 +1,56 @@
+const INPUT: &str = include_str!("input.txt");
+
+mod part_1;
+use part_1::part_1;
+mod part_2;
+use part_2::part_2;
+
+use std::str::FromStr;
+
+#[derive(Debug)]
+pub struct ParseError(String);
+#[derive(Debug)]
+pub struct Password {
+    pub first_num: usize,
+    pub second_num: usize,
+    pub letter: char,
+    pub password: String,
+}
+
+impl FromStr for Password {
+    type Err = ParseError;
+
+    fn from_str(line: &str) -> Result<Self, Self::Err> {
+        let parts = line.split(" ").collect::<Vec<_>>();
+
+        if parts.len() != 3 {
+            return Err(ParseError(line.into()));
+        }
+        let mut nums_iter = parts[0].split('-').map(|s| s.parse().unwrap());
+        let first_num = nums_iter.next().unwrap();
+        let second_num = nums_iter.next().unwrap();
+
+        let letter = parts[1].chars().nth(0).unwrap();
+        let password = parts[2].into();
+
+        Ok(Password {
+            first_num,
+            second_num,
+            letter,
+            password,
+        })
+    }
+}
+
+pub fn parse_input(input: &'static str) -> Vec<Password> {
+    input
+        .lines()
+        .map(|line| Password::from_str(line).unwrap())
+        .collect()
+}
+
+pub fn main() {
+    let input = parse_input(INPUT);
+    part_1(&input);
+    part_2(&input);
+}

rust/src/day02/part_1.rs

@@ -0,0 +1,30 @@
+pub(crate) fn part_1(input: &[crate::Password]) -> usize {
+    input.iter().fold(0, |acc, password| {
+        let num_letters = password
+            .password
+            .chars()
+            .filter(|&char| char == password.letter)
+            .count();
+        dbg!(password, num_letters);
+        if num_letters >= password.first_num && num_letters <= password.second_num {
+            acc + 1
+        } else {
+            acc
+        }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    const SAMPLE_INPUT: &str = include_str!("sample_input.txt");
+
+    #[test]
+    fn test_with_sample_solution() {
+        assert_eq!(super::part_1(&crate::parse_input(SAMPLE_INPUT)), 2);
+    }
+
+    #[test]
+    fn test_with_solution() {
+        assert_eq!(super::part_1(&crate::parse_input(crate::INPUT)), 620);
+    }
+}

rust/src/day02/part_2.rs

@@ -0,0 +1,42 @@
+pub(crate) fn part_2(input: &[crate::Password]) -> usize {
+    input.iter().fold(0, |acc, password| {
+        let first_char = password
+            .password
+            .chars()
+            .nth(password.first_num - 1) // 1-indexed
+            .unwrap_or_default();
+        let second_char = password
+            .password
+            .chars()
+            .nth(password.second_num - 1) // 1-indexed
+            .unwrap_or_default();
+        dbg!(
+            &password.password,
+            password.letter,
+            password.first_num,
+            first_char,
+            password.second_num,
+            second_char
+        );
+        if (password.letter == first_char) != (password.letter == second_char) {
+            acc + 1
+        } else {
+            acc
+        }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    const SAMPLE_INPUT: &str = include_str!("sample_input.txt");
+
+    #[test]
+    fn test_with_sample_solution() {
+        assert_eq!(super::part_2(&crate::parse_input(SAMPLE_INPUT)), 1);
+    }
+
+    #[test]
+    fn test_with_solution() {
+        assert_eq!(super::part_2(&crate::parse_input(crate::INPUT)), 727);
+    }
+}

rust/src/day02/sample_input.txt

@@ -0,0 +1,3 @@
+1-3 a: abcde
+1-3 b: cdefg
+2-9 c: ccccccccc