day 5 solution

src/day05.rs

@@ -0,0 +1,98 @@
+use anyhow::Result;
+use itertools::Itertools;
+
+#[derive(Debug)]
+struct LineSegment {
+    start: (isize, isize),
+    end: (isize, isize),
+}
+
+impl LineSegment {
+    fn is_horizontal_or_vertical(&self) -> bool {
+        self.start.0 == self.end.0 || self.start.1 == self.end.1
+    }
+
+    fn rasterize(&self) -> Vec<(isize, isize)> {
+        let xstep = (self.end.0 - self.start.0).signum();
+        let ystep = (self.end.1 - self.start.1).signum();
+        let mut ret = vec![self.start];
+        let (mut x, mut y) = self.start;
+        while (x, y) != self.end {
+            x += xstep;
+            y += ystep;
+            ret.push((x, y));
+        }
+        ret
+    }
+}
+
+fn parse_lines(input: &str) -> Vec<LineSegment> {
+    input
+        .lines()
+        .map(|l| {
+            let mut parts = l.split_whitespace();
+            let start_str = parts.next().unwrap();
+            let end_str = parts.nth(1).unwrap();
+            LineSegment {
+                start: start_str
+                    .split(',')
+                    .map(|s| s.parse::<isize>().unwrap())
+                    .collect_tuple()
+                    .unwrap(),
+                end: end_str
+                    .split(',')
+                    .map(|s| s.parse::<isize>().unwrap())
+                    .collect_tuple()
+                    .unwrap(),
+            }
+        })
+        .collect()
+}
+
+fn count_overlapped_cells(segments: &[LineSegment], includ_diag: bool) -> usize {
+    let mut marks: Vec<(isize, isize)> = segments
+        .iter()
+        .filter(|s| s.is_horizontal_or_vertical() || includ_diag)
+        .map(|s| s.rasterize())
+        .flatten()
+        .collect();
+    // sort so we can find duplicates
+    // **NOTE** IterTools has `.duplicates()` but it's significantly slower (more than 2x) than this
+    marks.sort_unstable();
+    marks[..]
+        .iter()
+        .zip(&marks[1..])
+        .filter(|(a, b)| a == b)
+        .unique()
+        .count()
+}
+
+pub(crate) fn run() -> Result<(usize, usize)> {
+    let input = include_str!("../data/day05.txt");
+    let segments = parse_lines(input);
+    Ok((
+        count_overlapped_cells(&segments, false),
+        count_overlapped_cells(&segments, true),
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example() {
+        let input = include_str!("../data/day05-test.txt");
+        let segments = parse_lines(input);
+        assert_eq!(count_overlapped_cells(&segments, false), 5);
+        assert_eq!(count_overlapped_cells(&segments, true), 12);
+    }
+
+    #[test]
+    fn test_my_data() {
+        let input = include_str!("../data/day05.txt");
+        let segments = parse_lines(input);
+        assert_eq!(count_overlapped_cells(&segments, false), 5124);
+        assert_eq!(count_overlapped_cells(&segments, true), 19771);
+    }
+}

src/main.rs

@@ -4,6 +4,7 @@ mod day01;
 mod day02;
 mod day03;
 mod day04;
+mod day05;
 mod utils;
 
 fn main() -> Result<()> {
@@ -11,5 +12,6 @@ fn main() -> Result<()> {
     println!("day02: {:?}", day02::run()?);
     println!("day03: {:?}", day03::run()?);
     println!("day04: {:?}", day04::run()?);
+    println!("day05: {:?}", day05::run()?);
     Ok(())
 }