Complete day 1

diff --git a/src/day01.rs b/src/day01.rs
new file mode 100644 (file)
index 0000000..b022310
--- /dev/null
+++ b/src/day01.rs
@@ -0,0 +1,75 @@
+use std::collections::HashMap;
+
+fn input() -> &'static str {
+    include_str!("../input/day01.txt")
+}
+
+fn parse(input: &str) -> (Vec<u32>, Vec<u32>) {
+    let mut left = vec![];
+    let mut right = vec![];
+    for (i, n) in input.split_whitespace().enumerate() {
+        if i % 2 == 0 {
+            left.push(n.parse::<u32>().unwrap())
+        } else {
+            right.push(n.parse::<u32>().unwrap())
+        }
+    }
+    (left, right)
+}
+
+fn distance(left: &mut [u32], right: &mut [u32]) -> u32 {
+    left.sort();
+    right.sort();
+    left.iter()
+        .zip(right.iter())
+        .map(|(l, r)| l.abs_diff(*r))
+        .sum()
+}
+
+fn similarity(left: &mut [u32], right: &mut [u32]) -> u32 {
+    let mut counts: HashMap<u32, u32> = HashMap::new();
+    for n in right {
+        let count = counts.entry(*n).or_default();
+        *count += 1;
+    }
+    left.iter().map(|n| n * counts.get(n).unwrap_or(&0)).sum()
+}
+
+pub fn part1() {
+    let (mut left, mut right) = parse(input());
+    let d = distance(&mut left, &mut right);
+    println!("Day 1 Part 1: {}", d);
+}
+
+pub fn part2() {
+    let (mut left, mut right) = parse(input());
+    let d = similarity(&mut left, &mut right);
+    println!("Day 1 Part 2: {}", d);
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    const INPUT_STR: &str = concat!("3   4\n", "4   3\n", "2   5\n", "1   3\n", "3   9\n", "3   3");
+
+    #[test]
+    fn test_parse() {
+        assert_eq!(
+            parse(INPUT_STR),
+            (vec![3, 4, 2, 1, 3, 3], vec![4, 3, 5, 3, 9, 3])
+        )
+    }
+
+    #[test]
+    fn test_distance() {
+        let (mut left, mut right) = parse(INPUT_STR);
+        assert_eq!(distance(&mut left, &mut right), 11)
+    }
+
+    #[test]
+    fn test_similarity() {
+        let (mut left, mut right) = parse(INPUT_STR);
+        assert_eq!(similarity(&mut left, &mut right), 31)
+    }
+}

diff --git a/src/main.rs b/src/main.rs
index f79c691f0853c5b08e114041f7c8db43b0452fe0..d54a6f67af3d6cbbeb023ee61023540421cc83c1 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,2 +1,6 @@
+pub mod day01;
+
 fn main() {
+    day01::part1();
+    day01::part2();
 }