day 1

data/examples/01.txt

@@ -0,0 +1,6 @@
+3   4
+4   3
+2   5
+1   3
+3   9
+3   3

src/bin/01.rs

@@ -0,0 +1,63 @@
+use std::collections::HashMap;
+
+advent_of_code::solution!(1);
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let (mut l, mut r): (Vec<i32>, Vec<i32>) = input
+        .lines()
+        .map(|l| {
+            let mut nums = l.split_whitespace().map(|n| n.parse::<i32>().unwrap());
+            (nums.next().unwrap(), nums.next().unwrap())
+        })
+        .unzip();
+
+    l.sort();
+    r.sort();
+
+    let sum: i32 = l.iter().zip(r.iter()).map(|(l, r)| (l - r).abs()).sum();
+    Some(sum as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let (l, r): (Vec<i32>, Vec<i32>) = input
+        .lines()
+        .map(|l| {
+            let mut nums = l.split_whitespace().map(|n| n.parse::<i32>().unwrap());
+            (nums.next().unwrap(), nums.next().unwrap())
+        })
+        .unzip();
+
+    let mut r_count: HashMap<i32, usize> = HashMap::new();
+
+    for n in r.iter() {
+        *r_count.entry(*n).or_insert(0) += 1;
+    }
+
+    let score: i32 = l
+        .iter()
+        .map(|&n| {
+            let count = *r_count.get(&n).unwrap_or(&0);
+            let score = n * count as i32;
+            score
+        })
+        .sum();
+
+    Some(score as u32)
+}
+
+#[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));
+    }
+}