1 files changed, 116 insertions, 0 deletions
diff --git a/src/bin/day5.rs b/src/bin/day5.rs
new file mode 100644
index 0000000..b396a6b
--- /dev/null
+++ b/src/bin/day5.rs
@@ -0,0 +1,116 @@
+use std::collections::HashMap;
+
+fn main() {
+    let input = advent::read_lines(5);
+    println!("5a: {}", count_overlaps(&input, false));
+    println!("5b: {}", count_overlaps(&input, true));
+}
+
+#[derive(PartialEq,Eq,Hash)]
+struct Point {
+    x: isize,
+    y: isize,
+}
+
+struct Line {
+    start: Point,
+    end: Point,
+}
+
+impl Point {
+    fn new(coord: &str) -> Point {
+        let (x_str, y_str) = coord.split_once(',').unwrap();
+        let x = x_str.parse::<isize>().unwrap();
+        let y = y_str.parse::<isize>().unwrap();
+        Point { x, y }
+    }
+}
+
+impl Line {
+    fn new(points: &str) -> Line {
+        let (start_str, end_str) = points.split_once(" -> ").unwrap();
+        let (start, end) = (Point::new(start_str), Point::new(end_str));
+        Line { start, end }
+    }
+
+    fn is_horizontal(&self) -> bool {
+        self.start.y == self.end.y
+    }
+
+    fn is_vertical(&self) -> bool {
+        self.start.x == self.end.x
+    }
+
+    fn points_on_line(&self) -> Vec<Point> {
+        let mut points = Vec::new();
+
+        let x_diff = self.end.x - self.start.x;
+        let y_diff = self.end.y - self.start.y;
+
+        if x_diff == 0 {
+            /* vertical line */
+            for y in 0 ..= y_diff.abs() {
+                points.push(Point { x: self.start.x, y: self.start.y + y_diff.signum() * y });
+            }
+        } else if y_diff == 0 {
+            /* horizontal line */
+            for x in 0 ..= x_diff.abs() {
+                points.push(Point { x: self.start.x + x_diff.signum() * x, y: self.start.y });
+            }
+        } else if x_diff.abs() == y_diff.abs() && x_diff.abs() > 0 {
+            /* diagonal line */
+            for i in 0 ..= x_diff.abs() {
+                let x = self.start.x + x_diff.signum() * i;
+                let y = self.start.y + y_diff.signum() * i;
+                points.push(Point { x, y });
+            }
+        } else {
+            panic!("No line!");
+        }
+
+        points
+    }
+}
+
+fn count_overlaps<T: AsRef<str>>(input: &[T], with_diagonal: bool) -> usize {
+    let lines : Vec<Line> = input.iter()
+                                 .map(|line| Line::new(line.as_ref()))
+                                 .collect();
+
+    let mut map = HashMap::new();
+    for line in lines {
+        if !with_diagonal && !line.is_horizontal() && !line.is_vertical() {
+            continue;
+        }
+        for point in line.points_on_line() {
+            let count = map.entry(point).or_insert(0);
+            *count += 1;
+        }
+    }
+    map.values()
+       .filter(|&count| *count > 1)
+       .count()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "0,9 -> 5,9",
+            "8,0 -> 0,8",
+            "9,4 -> 3,4",
+            "2,2 -> 2,1",
+            "7,0 -> 7,4",
+            "6,4 -> 2,0",
+            "0,9 -> 2,9",
+            "3,4 -> 1,4",
+            "0,0 -> 8,8",
+            "5,5 -> 8,2",
+        ];
+        assert_eq!(count_overlaps(&input, false), 5);
+        assert_eq!(count_overlaps(&input, true), 12);
+    }
+}