Christmas! 🎄

2 files changed, 55 insertions, 1 deletions

diff --git a/2018/src/day25.rs b/2018/src/day25.rs
new file mode 100644
index 0000000..1d992ec
--- /dev/null
+++ b/2018/src/day25.rs
@@ -0,0 +1,52 @@
+use std::io;
+use std::io::BufRead;
+
+type Point = (i32, i32, i32, i32);
+
+fn dist(a: &Point, b: &Point) -> i32 {
+    (a.0 - b.0).abs() + (a.1 - b.1).abs() + (a.2 - b.2).abs() + (a.3 - b.3).abs()
+}
+
+fn flood(pts: &[Point], comp: &mut [i32], at: usize, id: i32) {
+    if comp[at] != -1 {
+        assert!(comp[at] == id);
+        return;
+    }
+
+    comp[at] = id;
+
+    for i in 0..pts.len() {
+        if dist(&pts[at], &pts[i]) <= 3 {
+            flood(pts, comp, i, id);
+        }
+    }
+}
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
+    let pts = reader.lines().map(|l| {
+        let line = l.unwrap();
+        let mut spl = line.split(',');
+        let x = spl.next().unwrap().parse().unwrap();
+        let y = spl.next().unwrap().parse().unwrap();
+        let z = spl.next().unwrap().parse().unwrap();
+        let w = spl.next().unwrap().parse().unwrap();
+        (x, y, z, w)
+    }).collect::<Vec<_>>();
+
+    let mut comp = vec![-1; pts.len()];
+
+    let mut ncomps = 0;
+
+    for i in 0..pts.len() {
+        if comp[i] != -1 {
+            continue;
+        }
+
+        flood(&pts, &mut comp, i, ncomps);
+        ncomps += 1;
+    }
+
+    let part1 = ncomps;
+
+    Ok((part1.to_string(), String::new()))
+}
diff --git a/2018/src/main.rs b/2018/src/main.rs
index 85021fe..9d26e8f 100644
--- a/2018/src/main.rs
+++ b/2018/src/main.rs
@@ -30,8 +30,9 @@ mod day21;
 mod day22;
 mod day23;
 mod day24;
+mod day25;
 
-static NUM_DAYS: i32 = 24;
+static NUM_DAYS: i32 = 25;
 
 fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
     match day {
@@ -59,6 +60,7 @@ fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
         22 => day22::main(reader),
         23 => day23::main(reader),
         24 => day24::main(reader),
+        25 => day25::main(reader),
         _ => Err(Error::new(ErrorKind::Other, "Invalid day"))
     }
 }