2021: day05: part 1

aoc2021/src/day05.rs

@@ -0,0 +1,108 @@
+use std::collections::HashMap;
+use std::fmt::Write;
+use std::iter;
+
+use anyhow::{Context, Result};
+
+const INPUT: &str = include_str!("../input/day05.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<usize> {
+    let lines = input
+        .lines()
+        .map(str::parse::<Line>)
+        .collect::<Result<Vec<_>>>()?;
+
+    let mut grid = HashMap::new();
+
+    lines
+        .iter()
+        .filter(|l| l.is_horizontal() || l.is_vertical())
+        .for_each(|l| {
+            for cell in l.cells() {
+                *grid.entry(cell).or_insert(0) += 1;
+            }
+        });
+
+    Ok(grid.into_values().filter(|c| *c > 1).count())
+}
+
+#[derive(Debug)]
+struct Line {
+    from: (usize, usize),
+    to: (usize, usize),
+}
+
+impl Line {
+    fn is_horizontal(&self) -> bool {
+        self.to.1 == self.from.1
+    }
+
+    fn is_vertical(&self) -> bool {
+        self.to.0 == self.from.0
+    }
+
+    fn cells(&self) -> Box<dyn Iterator<Item = (usize, usize)>> {
+        if self.is_horizontal() {
+            let min = self.from.0.min(self.to.0);
+            let max = self.from.0.max(self.to.0);
+            Box::new((min..=max).zip(iter::repeat(self.from.1)))
+                as Box<dyn Iterator<Item = (usize, usize)>>
+        } else {
+            let min = self.from.1.min(self.to.1);
+            let max = self.from.1.max(self.to.1);
+            Box::new(iter::repeat(self.from.0).zip(min..=max))
+                as Box<dyn Iterator<Item = (usize, usize)>>
+        }
+    }
+}
+
+impl std::str::FromStr for Line {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        let (from, to) = s
+            .split_once(" -> ")
+            .context("couldn't parse line: missing ` -> `")?;
+
+        let from = {
+            let (x, y) = from
+                .split_once(',')
+                .context("couldn't parse line origin: missing `,`")?;
+            (x.parse()?, y.parse()?)
+        };
+
+        let to = {
+            let (x, y) = to
+                .split_once(',')
+                .context("couldn't parse line origin: missing `,`")?;
+            (x.parse()?, y.parse()?)
+        };
+
+        Ok(Line { from, to })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED: &str = include_str!("../input/day05_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 5);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 4745);
+    }
+}

aoc2021/src/lib.rs

@@ -4,3 +4,4 @@ pub mod day01;
 pub mod day02;
 pub mod day03;
 pub mod day04;
+pub mod day05;

aoc2021/src/main.rs

@@ -6,9 +6,10 @@ use aoc2021::day01;
 use aoc2021::day02;
 use aoc2021::day03;
 use aoc2021::day04;
+use aoc2021::day05;
 
 fn main() -> Result<()> {
-    let days: &[DayFunc] = &[day01::run, day02::run, day03::run, day04::run];
+    let days: &[DayFunc] = &[day01::run, day02::run, day03::run, day04::run, day05::run];
 
     aoc::run(days)
 }