2018 day 25

Author: ictrobot

crates/utils/src/geometry.rs

@@ -1,4 +1,4 @@
-//! 2D & 3D vector implementations.
+//! 2D, 3D and 4D vector implementations.
 
 use crate::number::{Integer, Number, Signed, UnsignedInteger};
 use std::fmt::Debug;
@@ -217,6 +217,12 @@ vec_impl! {3, (T, T, T) =>
     pub struct Vec3{0 => x, 1 => y, 2 => z}
 }
 
+vec_impl! {4, (T, T, T, T) =>
+    /// Struct representing a 4D vector or point.
+    #[doc(alias("Vector4", "Point4", "Point4D"))]
+    pub struct Vec4{0 => x, 1 => y, 2 => z, 3 => w}
+}
+
 /// Enum representing the four cardinal directions.
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 #[repr(u8)]

crates/year2018/examples/day25_example0.txt

@@ -0,0 +1,10 @@
+-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

crates/year2018/examples/day25_example1.txt

@@ -0,0 +1,10 @@
+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

crates/year2018/examples/day25_example2.txt

@@ -0,0 +1,10 @@
+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

crates/year2018/src/day25.rs

@@ -0,0 +1,54 @@
+use utils::geometry::Vec4;
+use utils::prelude::*;
+
+/// Clustering points within Manhattan distance.
+#[derive(Clone, Debug)]
+pub struct Day25 {
+    points: Vec<Vec4<i32>>,
+}
+
+impl Day25 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let mut points = parser::i32()
+            .repeat_n(b',')
+            .map(Vec4::from)
+            .parse_lines(input)?;
+
+        points.sort_unstable_by_key(|p| p.x);
+
+        Ok(Self { points })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u32 {
+        let mut remaining = self.points.clone();
+        let mut to_visit = Vec::with_capacity(remaining.len());
+        let mut constellations = 0;
+        while let Some(start) = remaining.pop() {
+            to_visit.push(start);
+            while let Some(point) = to_visit.pop() {
+                // Use binary search to only check points in range on the x-axis.
+                // This requires keeping the remaining points sorted (instead of using swap_remove)
+                let start = remaining.partition_point(|p| p.x < point.x - 3);
+                let end = remaining.partition_point(|p| p.x <= point.x + 3);
+
+                to_visit.extend(
+                    remaining.extract_if(start..end, |p| p.manhattan_distance_to(point) <= 3),
+                );
+            }
+            constellations += 1;
+        }
+        constellations
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> &'static str {
+        "🎄"
+    }
+}
+
+examples!(Day25 -> (u32, &'static str) [
+    {file: "day25_example0.txt", part1: 4},
+    {file: "day25_example1.txt", part1: 3},
+    {file: "day25_example2.txt", part1: 8},
+]);

crates/year2018/src/lib.rs

@@ -28,4 +28,5 @@ utils::year!(2018 => year2018, ${
     22 => day22::Day22,
     23 => day23::Day23,
     24 => day24::Day24,
+    25 => day25::Day25,
 });