Day 25 part 1.

src/main.rs

@@ -1,3 +1,3 @@
 fn main() {
-    aoc_2018::tasks::day18::task2();
+    aoc_2018::tasks::day25::task1();
 }

src/tasks/day25.rs

@@ -0,0 +1,138 @@
+use std::collections::VecDeque;
+
+use crate::utils;
+
+pub fn task1() {
+    println!("{}", solve(&utils::read_file("input/day25.txt")));
+}
+
+fn solve(input: &str) -> u32 {
+    let mut points: Vec<STP> = input.lines().map(STP::from).collect();
+    let mut constellations = 0;
+    while let Some(next_origin) = points.pop() {
+        constellations += 1;
+        let mut queue = VecDeque::new();
+        queue.push_back(next_origin);
+
+        while let Some(next) = queue.pop_front() {
+            let (neighbors, remainder) = points.into_iter().partition(|p| next.is_neighbor_to(p));
+            points = remainder;
+            for n in neighbors {
+                queue.push_back(n);
+            }
+        }
+    }
+    constellations
+}
+
+#[derive(Hash, Eq, PartialEq, Debug)]
+struct STP(i32, i32, i32, i32);
+
+impl STP {}
+
+impl STP {
+    fn neighbors(&self) -> Vec<Self> {
+        let mut result = Vec::new();
+        for x in -3..=3 {
+            for y in -3..=3 {
+                for z in -3..=3 {
+                    for t in -3..=3 {
+                        let candidate = STP(self.0 + x, self.1 + y, self.2 + z, self.3 + t);
+                        if self.is_neighbor_to(&candidate) {
+                            result.push(candidate);
+                        }
+                    }
+                }
+            }
+        }
+        result
+    }
+
+    fn distance(&self, other: &Self) -> u32 {
+        ((self.0 - other.0).abs()
+            + (self.1 - other.1).abs()
+            + (self.2 - other.2).abs()
+            + (self.3 - other.3).abs()) as u32
+    }
+
+    fn is_neighbor_to(&self, other: &Self) -> bool {
+        self.distance(other) <= 3
+    }
+}
+
+impl From<&str> for STP {
+    fn from(value: &str) -> Self {
+        let mut split = value.split(",");
+
+        STP(
+            split.next().unwrap().parse().unwrap(),
+            split.next().unwrap().parse().unwrap(),
+            split.next().unwrap().parse().unwrap(),
+            split.next().unwrap().parse().unwrap(),
+        )
+    }
+}
+
+mod test {
+    use crate::tasks::day25::solve;
+
+    #[test]
+    fn example1() {
+        let input = "0,0,0,0
+3,0,0,0
+0,3,0,0
+0,0,3,0
+0,0,0,3
+0,0,0,6
+9,0,0,0
+12,0,0,0";
+        assert_eq!(solve(input), 2);
+    }
+
+    #[test]
+    fn example2() {
+        let input = "-1,2,2,0
+0,0,2,-2
+0,0,0,-2
+-1,2,0,0
+-2,-2,-2,2
+3,0,2,-1
+-1,3,2,2
+-1,0,-1,0
+0,2,1,-2
+3,0,0,0";
+        assert_eq!(solve(input), 4);
+    }
+
+    #[test]
+    fn example3() {
+        let input = "1,-1,0,1
+2,0,-1,0
+3,2,-1,0
+0,0,3,1
+0,0,-1,-1
+2,3,-2,0
+-2,2,0,0
+2,-2,0,-1
+1,-1,0,-1
+3,2,0,2
+";
+        assert_eq!(solve(input), 3);
+    }
+
+    #[test]
+    fn example4() {
+        let input = "1,-1,-1,-2
+-2,-2,0,1
+0,2,1,3
+-2,3,-2,1
+0,2,3,-2
+-1,-1,1,-2
+0,-2,-1,0
+-2,2,3,-1
+1,2,2,0
+-1,-2,0,-2
+";
+        assert_eq!(solve(input), 8);
+    }
+}

src/tasks/mod.rs

@@ -19,3 +19,4 @@ pub mod day20;
 pub mod day22;
 pub mod day23;
 pub mod day24;
+pub mod day25;