AOC 2024 Day 01

Author: raul-sauco

aoc/2024/rust/data/examples/01.txt

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

aoc/2024/rust/src/bin/01.rs

@@ -0,0 +1,63 @@
+use std::{collections::HashMap, i32, u32};
+
+advent_of_code::solution!(1);
+
+fn parse(input: &str) -> (Vec<i32>, Vec<i32>) {
+    input
+        .lines()
+        .map(|line| {
+            let mut nums = line
+                .split_whitespace()
+                .map(|s| s.parse::<i32>().expect("A valid parse"));
+            let left = nums.next().expect("A value on the left column");
+            let right = nums.next().expect("A value on the right column");
+            (left, right)
+        })
+        .collect::<Vec<_>>() // Propagate the error if any
+        .into_iter()
+        .unzip()
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let (mut col1, mut col2) = parse(&input);
+    col1.sort_unstable();
+    col2.sort_unstable();
+    Some(
+        col1.into_iter()
+            .zip(col2.into_iter())
+            .map(|(a, b)| (a - b).abs() as u32)
+            .sum::<u32>(),
+    )
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let (col1, col2) = parse(&input);
+    let mut counts = HashMap::new();
+    for num in col2 {
+        counts.entry(num).and_modify(|c| *c += 1).or_insert(1);
+    }
+    Some(col1.into_iter().fold(0, |acc, x| {
+        if let Some(&right_count) = counts.get(&x) {
+            acc + (x * right_count) as u32
+        } else {
+            acc
+        }
+    }))
+}
+
+#[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));
+    }
+}