feat: add day 1

src/bin/01.rs

@@ -0,0 +1,68 @@
+advent_of_code::solution!(1);
+
+use std::collections::HashMap;
+
+fn parse_line(input: &str) -> (u32, u32) {
+    let input = input
+        .split_whitespace()
+        .filter(|s| !s.is_empty())
+        .collect::<Vec<&str>>();
+    let input = input.as_slice();
+    match input {
+        [a, b] => (
+            a.parse::<u32>().expect("parse error"),
+            b.parse::<u32>().expect("parse error"),
+        ),
+        _ => panic!("parse error!"),
+    }
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let (mut left, mut right): (Vec<_>, Vec<_>) = input
+        .strip_suffix("\n")
+        .unwrap_or(input)
+        .lines()
+        .map(parse_line)
+        .unzip();
+    left.sort();
+    right.sort();
+    left.into_iter()
+        .zip(right)
+        .map(|(a, b)| a.abs_diff(b))
+        .sum::<u32>()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let (left, right): (Vec<_>, Vec<_>) = input
+        .strip_suffix("\n")
+        .unwrap_or(input)
+        .lines()
+        .map(parse_line)
+        .unzip();
+    let mut right_count: HashMap<u32, u8> = HashMap::new();
+    right
+        .iter()
+        .for_each(|u| *right_count.entry(*u).or_default() += 1);
+    left.into_iter()
+        .map(|c| c * *right_count.entry(c).or_default() as u32)
+        .sum::<u32>()
+        .into()
+}
+
+#[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(11));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(31));
+    }
+}