day23 part 2 correct intersection test (speed up by factor 2, yay!)

src/tasks/day23.rs

@@ -138,41 +138,6 @@ impl Bot {
     fn dist(&self, p: &Point) -> isize {
         self.center.distance(&p)
     }
-
-    fn corners(&self) -> Vec<Point> {
-        vec![
-            Point {
-                x: self.center.x + self.range as isize,
-                y: self.center.y,
-                z: self.center.z,
-            },
-            Point {
-                x: self.center.x - self.range as isize,
-                y: self.center.y,
-                z: self.center.z,
-            },
-            Point {
-                x: self.center.x,
-                y: self.center.y + self.range as isize,
-                z: self.center.z,
-            },
-            Point {
-                x: self.center.x,
-                y: self.center.y - self.range as isize,
-                z: self.center.z,
-            },
-            Point {
-                x: self.center.x,
-                y: self.center.y,
-                z: self.center.z + self.range as isize,
-            },
-            Point {
-                x: self.center.x,
-                y: self.center.y,
-                z: self.center.z - self.range as isize,
-            },
-        ]
-    }
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
@@ -229,69 +194,16 @@ impl Cube {
         ]
     }
 
-    fn corners(&self) -> Vec<Point> {
-        vec![
-            Point::new(
-                self.base.x + self.len,
-                self.base.y + self.len,
-                self.base.z + self.len,
-            ),
-            Point::new(
-                self.base.x + self.len - 1,
-                self.base.y + self.len - 1,
-                self.base.z,
-            ),
-            Point::new(
-                self.base.x + self.len - 1,
-                self.base.y,
-                self.base.z + self.len - 1,
-            ),
-            Point::new(self.base.x + self.len - 1, self.base.y, self.base.z),
-            Point::new(
-                self.base.x,
-                self.base.y + self.len - 1,
-                self.base.z + self.len - 1,
-            ),
-            Point::new(self.base.x, self.base.y + self.len - 1, self.base.z),
-            Point::new(self.base.x, self.base.y, self.base.z + self.len - 1),
-            Point::new(self.base.x, self.base.y, self.base.z),
-        ]
-    }
-
     fn intersects(&self, bot: &Bot) -> bool {
-        if self
+        ((self.base.x - bot.center.x).abs()
-            .corners()
+            + (self.base.x + self.len - bot.center.x).abs()
-            .iter()
+            + (self.base.y - bot.center.y).abs()
-            .any(|corner| corner.distance(&bot.center) <= bot.range)
+            + (self.base.y + self.len - bot.center.y).abs()
-        {
+            + (self.base.z - bot.center.z).abs()
-            return true;
+            + (self.base.z + self.len - bot.center.z).abs()
-        }
+            - 3 * self.len)
-        if bot
+            / 2
-            .corners()
+            <= bot.range
-            .iter()
-            .any(|corner| self.contains_point(&corner))
-        {
-            return true;
-        }
-
-        // WARNING this is a conservative check! it omits the case where no
-        // corners of the octahedron/cube are within each other:
-        // +-----+
-        // |     |/\
-        // |    /|  \
-        // +---/-+   \
-        // although this is just a wrong 2D example, in 3D that could happen.
-
-        false
-    }
-
-    fn contains_point(&self, p: &Point) -> bool {
-        self.base.x <= p.x
-            && self.base.x + self.len > p.x
-            && self.base.y <= p.y
-            && self.base.y + self.len > p.y
-            && self.base.z <= p.z
-            && self.base.z + self.len > p.z
     }
 }