2021: day07: part 1

aoc2021/src/day07.rs

@@ -0,0 +1,48 @@
+use std::fmt::Write;
+
+use anyhow::{Context, Result};
+
+const INPUT: &str = include_str!("../input/day07.txt");
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let mut horizontal_positions = input
+        .trim()
+        .split(',')
+        .map(|n| n.parse::<u64>().context("couldn't parse position"))
+        .collect::<Result<Vec<_>>>()?;
+
+    // TODO: try linear selection algorithm
+    horizontal_positions.sort_unstable();
+    let median = horizontal_positions[horizontal_positions.len() / 2];
+
+    Ok(horizontal_positions
+        .iter()
+        // TODO: use abs_diff when stabilized
+        .map(|n| n.max(&median) - n.min(&median))
+        .sum())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED: &str = include_str!("../input/day07_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 37);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 340056);
+    }
+}

aoc2021/src/lib.rs

@@ -6,3 +6,4 @@ pub mod day03;
 pub mod day04;
 pub mod day05;
 pub mod day06;
+pub mod day07;

aoc2021/src/main.rs

@@ -8,6 +8,7 @@ use aoc2021::day03;
 use aoc2021::day04;
 use aoc2021::day05;
 use aoc2021::day06;
+use aoc2021::day07;
 
 fn main() -> Result<()> {
     let days: &[DayFunc] = &[
@@ -17,6 +18,7 @@ fn main() -> Result<()> {
         day04::run,
         day05::run,
         day06::run,
+        day07::run,
     ];
 
     aoc::run(days)