1 files changed, 89 insertions, 0 deletions
diff --git a/2017/src/bin/day_20.rs b/2017/src/bin/day_20.rs
new file mode 100644
index 0000000..f528675
--- /dev/null
+++ b/2017/src/bin/day_20.rs
@@ -0,0 +1,89 @@
+extern crate advent_of_code_2017;
+use advent_of_code_2017::*;
+
+extern crate regex;
+use regex::Regex;
+
+#[macro_use]
+extern crate lazy_static;
+
+use std::str::FromStr;
+
+fn main() {
+    let args = AdventArgs::init();
+
+    let mut particles: Vec<Particle> = args.input.iter()
+        .map(|line| line.parse().unwrap())
+        .collect();
+
+    // I took eventually to be after a largish number. Seemed to work
+    // out, but I'm sure there is a more mathematical way to work it
+    // out.
+    for _ in 0..1000 {
+        particles = particles.iter().map(|p| p.step()).collect();
+        if args.part == 2 {
+            let before_collisions = particles.clone();
+            particles.retain(|p| {
+                before_collisions.iter().filter(|p2| p2.position == p.position).count() == 1
+            });
+        }
+    }
+
+    if args.part == 1 {
+        let (closest, _) = particles.iter().enumerate().min_by_key(|&(_, p)| p.position.manhattan_distance()).unwrap();
+        println!("Closest to 0: {}", closest);
+    } else {
+        let remaining = particles.iter().count();
+        println!("Remaining: {}", remaining);
+    }
+
+}
+
+#[derive(Debug, Clone)]
+struct Particle {
+    position: Point3d,
+    velocity: Point3d,
+    acceleration: Point3d
+}
+
+
+impl Particle {
+    fn step(&self) -> Particle {
+        let v = self.velocity + self.acceleration;
+        Particle {
+            position: self.position + v,
+            velocity: v,
+            acceleration: self.acceleration
+        }
+    }
+}
+
+impl FromStr for Particle {
+    type Err = String;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        lazy_static!{
+            static ref RE: Regex = Regex::new(r"p=<(-?\d+),(-?\d+),(-?\d+)>, v=<(-?\d+),(-?\d+),(-?\d+)>, a=<(-?\d+),(-?\d+),(-?\d+)>").unwrap();
+        };
+        
+        let caps = RE.captures(s).unwrap();
+        Ok(Particle {
+            position: Point3d {
+                x: caps[1].parse().unwrap(),
+                y: caps[2].parse().unwrap(),
+                z: caps[3].parse().unwrap()
+            },
+            velocity: Point3d {
+                x: caps[4].parse().unwrap(),
+                y: caps[5].parse().unwrap(),
+                z: caps[6].parse().unwrap()
+            },
+            acceleration: Point3d {
+                x: caps[7].parse().unwrap(),
+                y: caps[8].parse().unwrap(),
+                z: caps[9].parse().unwrap()
+            }
+        })
+    }
+}
+