feat(day1): init

src/solutions/day_01.rs

@@ -0,0 +1,74 @@
+use itertools::Itertools;
+
+use crate::common::{Answer, Solution};
+
+pub struct Day01;
+
+impl Solution for Day01 {
+    fn name(&self) -> &'static str {
+        "Historian Hysteria"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let (mut left, mut right) = input
+            .lines()
+            .map(|l| l.split_once("   ").unwrap())
+            .map(|(n1, n2)| (n1.parse::<i32>().unwrap(), n2.parse::<i32>().unwrap()))
+            .collect::<(Vec<_>, Vec<_>)>();
+
+        left.sort();
+        right.sort();
+
+        let sum: i32 = left
+            .into_iter()
+            .zip(right)
+            .map(|(a, b)| (a - b).abs())
+            .sum();
+
+        Answer::Number(sum as u64)
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        let (left, right) = input
+            .lines()
+            .map(|l| l.split_once("   ").unwrap())
+            .map(|(n1, n2)| (n1.parse::<i32>().unwrap(), n2.parse::<i32>().unwrap()))
+            .collect::<(Vec<_>, Vec<_>)>();
+
+        let counts = right.into_iter().counts();
+
+        let sum = left
+            .into_iter()
+            .map(|n| counts.get(&n).unwrap_or(&0) * (n as usize))
+            .sum::<usize>();
+
+        Answer::Number(sum as u64)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::Day01;
+    use crate::common::Solution;
+
+    use indoc::indoc;
+
+    const INPUT: &str = indoc! {"
+        3   4
+        4   3
+        2   5
+        1   3
+        3   9
+        3   3
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day01.part_a(INPUT), 11.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day01.part_b(INPUT), 31.into());
+    }
+}

src/solutions/mod.rs

@@ -1,3 +1,5 @@
 use crate::common::Solution;
 
-pub const SOLUTIONS: &[&dyn Solution] = &[];
+mod day_01;
+
+pub const SOLUTIONS: &[&dyn Solution] = &[&day_01::Day01];