1 files changed, 125 insertions, 0 deletions
diff --git a/src/day_5.rs b/src/day_5.rs
new file mode 100644
index 0000000..acd2ac1
--- /dev/null
+++ b/src/day_5.rs
@@ -0,0 +1,125 @@
+use std::cmp;
+use std::convert::Infallible;
+use std::str::FromStr;
+
+const SIZE: usize = 1000;
+
+#[derive(Debug)]
+struct Line
+{
+    pub a: (u32, u32),
+    pub b: (u32, u32),
+}
+
+fn part1(input: &[Line])
+{
+    let mut map = [[0; SIZE]; SIZE];
+    for line in input {
+        line.cast_vh(&mut map);
+    }
+
+    let num_intersections = map.iter().flatten().filter(|&n| *n >= 2).count();
+    println!("Solution part 1: {}", num_intersections);
+}
+
+fn part2(input: &[Line])
+{
+    let mut map = [[0; SIZE]; SIZE];
+    for line in input {
+        line.cast_vh(&mut map);
+        line.cast_diag(&mut map);
+    }
+
+    let num_intersections = map.iter().flatten().filter(|&n| *n >= 2).count();
+    println!("Solution part 2: {}", num_intersections);
+}
+
+pub fn run(input: Vec<String>)
+{
+    let lines: Vec<Line> = input.iter().map(|s| Line::from_str(s).unwrap()).collect();
+
+    part1(&lines);
+    part2(&lines);
+}
+
+impl Line
+{
+    pub fn is_horizontal(&self) -> bool { self.a.1 == self.b.1 }
+
+    pub fn is_vertical(&self) -> bool { self.a.0 == self.b.0 }
+
+    pub fn cast_vh(&self, onto: &mut [[u8; SIZE]])
+    {
+        if self.is_horizontal() {
+            let start = cmp::min(self.a.0, self.b.0);
+            let end = cmp::max(self.a.0, self.b.0);
+            for x in start..=end {
+                onto[self.a.1 as usize][x as usize] += 1;
+            }
+        }
+        else if self.is_vertical() {
+            let start = cmp::min(self.a.1, self.b.1);
+            let end = cmp::max(self.a.1, self.b.1);
+            for y in start..=end {
+                onto[y as usize][self.a.0 as usize] += 1;
+            }
+        }
+    }
+
+    pub fn cast_diag(&self, onto: &mut [[u8; SIZE]])
+    {
+        if self.is_horizontal() || self.is_vertical() {
+            return;
+        }
+
+        // We know all other lines are 45 deg
+        let mut dir = (0, 0);
+        let len: i32 = if self.a.0 < self.b.0 {
+            dir.0 = 1;
+            (self.b.0 - self.a.0) as i32
+        }
+        else if self.a.0 > self.b.0 {
+            dir.0 = -1;
+            (self.a.0 - self.b.0) as i32
+        }
+        else {
+            panic!("line is unexpectedly vertical!");
+        };
+        if self.a.1 < self.b.1 {
+            dir.1 = 1;
+        }
+        else if self.a.1 > self.b.1 {
+            dir.1 = -1;
+        }
+        else {
+            panic!("line is unexpectedly horizontal!");
+        }
+
+        for i in 0..=len {
+            onto[(self.a.1 as i32 + (i * dir.1)) as usize]
+                [(self.a.0 as i32 + (i * dir.0)) as usize] += 1;
+        }
+    }
+}
+
+impl FromStr for Line
+{
+    type Err = Infallible;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err>
+    {
+        let parse_point = |s: &str| {
+            let nums: Vec<u32> = s.split(',').map(|s| s.parse().unwrap()).collect();
+            assert_eq!(nums.len(), 2);
+            (nums[0], nums[1])
+        };
+
+        let points: Vec<(u32, u32)> = s.split(" -> ").map(|s| parse_point(s)).collect();
+        assert_eq!(points.len(), 2);
+
+        Ok(Line {
+            a: points[0],
+            b: points[1],
+        })
+    }
+}