2024: Day 1, part 1

2024/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "advent-of-code"
+version = "0.1.0"

2024/Cargo.toml

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+[package]
+name = "advent-of-code"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

2024/src/day1.rs

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+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::path::Path;
+
+pub fn main(input: &Path) {
+    let file = BufReader::new(File::open(input).expect("unable to open input"));
+
+    let mut group1 = Vec::new();
+    let mut group2 = Vec::new();
+
+    for line in file.lines() {
+        let line = line.expect("error reading input line");
+        let mut split = line.split_ascii_whitespace();
+        let mut next = || split.next().unwrap().parse::<i32>().unwrap();
+        group1.push(next());
+        group2.push(next());
+    }
+
+    group1.sort();
+    group2.sort();
+
+    let part1: i32 = group1
+        .iter()
+        .copied()
+        .zip(group2.iter().copied())
+        .map(|(a, b)| (a - b).abs())
+        .sum();
+
+    println!("Part 1: {part1}");
+}

2024/src/main.rs

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+use std::env;
+use std::path::PathBuf;
+
+mod day1;
+
+fn main() {
+    let Some(input) = env::args().skip(1).next().map(PathBuf::from) else {
+        eprintln!("Usage advent-of-code dayN.txt");
+        return;
+    };
+
+    let day = input
+        .file_stem()
+        .and_then(|stem| stem.to_str())
+        .and_then(|stem| stem.strip_prefix("day").unwrap_or(stem).parse::<u8>().ok());
+    let Some(day) = day else {
+        eprintln!("Unable to determine day from {}", input.display());
+        return;
+    };
+
+    match day {
+        1 => day1::main(&input),
+        _ => {
+            eprintln!("Unknown day {day}");
+            return;
+        }
+    }
+}