Day 18 part 2

diff --git a/src/day18.rs b/src/day18.rs
index a75ddb7..9614166 100644 (file)
--- a/src/day18.rs
+++ b/src/day18.rs
@@ -4,6 +4,15 @@ pub struct Cube {
     z: i32,
 }
 
+#[derive(Clone, Copy)]
+pub enum Element {
+    Empty,
+    Obsidian,
+    Droplet,
+}
+
+type Mat3D = Vec<Vec<Vec<Element>>>;
+
 pub fn parse(input: &str) -> Vec<Cube> {
     input
         .lines()
@@ -22,8 +31,17 @@ pub fn parse(input: &str) -> Vec<Cube> {
         .collect()
 }
 
-pub fn surface(cubes: &[Cube]) -> i32 {
-    let mut matrix: Vec<Vec<Vec<bool>>> = Vec::new();
+static NEIGHBOURS: [(i32, i32, i32); 6] = [
+    (1, 0, 0),
+    (-1, 0, 0),
+    (0, 1, 0),
+    (0, -1, 0),
+    (0, 0, 1),
+    (0, 0, -1),
+];
+
+pub fn surface(cubes: &[Cube]) -> (i32, Mat3D) {
+    let mut matrix: Mat3D = Vec::new();
 
     for c in cubes {
         for _ in matrix.len()..=c.x as usize {
@@ -33,24 +51,17 @@ pub fn surface(cubes: &[Cube]) -> i32 {
             matrix[c.x as usize].push(Vec::new())
         }
         for _ in matrix[c.x as usize][c.y as usize].len()..=c.z as usize {
-            matrix[c.x as usize][c.y as usize].push(false)
+            matrix[c.x as usize][c.y as usize].push(Element::Empty)
         }
-        matrix[c.x as usize][c.y as usize][c.z as usize] = true;
+        matrix[c.x as usize][c.y as usize][c.z as usize] = Element::Obsidian;
     }
 
     let mut surface: i32 = 0;
     for x in 0..matrix.len() as i32 {
         for y in 0..matrix[x as usize].len() as i32 {
             for z in 0..matrix[x as usize][y as usize].len() as i32 {
-                if matrix[x as usize][y as usize][z as usize] {
-                    for (dx, dy, dz) in [
-                        (1, 0, 0),
-                        (-1, 0, 0),
-                        (0, 1, 0),
-                        (0, -1, 0),
-                        (0, 0, 1),
-                        (0, 0, -1),
-                    ] {
+                if let Element::Obsidian = matrix[x as usize][y as usize][z as usize] {
+                    for (dx, dy, dz) in NEIGHBOURS {
                         let (x, y, z) = (x + dx, y + dy, z + dz);
                         if x < 0
                             || x >= matrix.len() as i32
@@ -58,9 +69,9 @@ pub fn surface(cubes: &[Cube]) -> i32 {
                             || y >= matrix[x as usize].len() as i32
                             || z < 0
                             || z >= matrix[x as usize][y as usize].len() as i32
-                            || !matrix[x as usize][y as usize][z as usize]
+                            || matches!(matrix[x as usize][y as usize][z as usize], Element::Empty)
                         {
-                            surface = surface + 1;
+                            surface += 1;
                         }
                     }
                 }
@@ -68,11 +79,69 @@ pub fn surface(cubes: &[Cube]) -> i32 {
         }
     }
 
-    surface
+    (surface, matrix)
 }
 
-pub fn surface_without_trapped_air(cubes: &[Cube]) -> i32 {
-    0 // TODO
+enum FloodResult {
+    TouchingLimits,
+    InnerSurface(i32),
+}
+
+fn flood(m: &mut Mat3D, x: i32, y: i32, z: i32) -> FloodResult {
+    let mut to_visit = vec![(x, y, z)];
+    let mut surface = 0;
+    let mut touching_limits = false;
+
+    while let Some((x, y, z)) = to_visit.pop() {
+        if let Element::Droplet = m[x as usize][y as usize][z as usize] {
+            continue;
+        }
+
+        m[x as usize][y as usize][z as usize] = Element::Droplet;
+        for (dx, dy, dz) in NEIGHBOURS {
+            let (x, y, z) = (x + dx, y + dy, z + dz);
+            if x < 0
+                || x >= m.len() as i32
+                || y < 0
+                || y >= m[x as usize].len() as i32
+                || z < 0
+                || z >= m[x as usize][y as usize].len() as i32
+            {
+                touching_limits = true;
+                continue;
+            }
+            match m[x as usize][y as usize][z as usize] {
+                Element::Empty => to_visit.push((x, y, z)),
+                Element::Obsidian => surface += 1,
+                Element::Droplet => (),
+            }
+        }
+    }
+
+    if touching_limits {
+        FloodResult::TouchingLimits
+    } else {
+        FloodResult::InnerSurface(surface)
+    }
+}
+
+pub fn surface_without_trapped_air(outer_surface: i32, mut m: Mat3D) -> i32 {
+    let mut inner_surface = 0;
+    for x in 0..m.len() {
+        for y in 0..m[x].len() {
+            for z in 0..m[x][y].len() {
+                if let Element::Empty = m[x][y][z] {
+                    if let FloodResult::InnerSurface(s) =
+                        flood(&mut m, x as i32, y as i32, z as i32)
+                    {
+                        inner_surface += s;
+                    }
+                }
+            }
+        }
+    }
+
+    outer_surface - inner_surface
 }
 
 #[cfg(test)]
@@ -96,9 +165,14 @@ mod tests {
     #[test]
     fn part1() {
         let cubes = parse(CUBES);
-        assert_eq!(surface(&cubes), 64);
+        let (surface, _) = surface(&cubes);
+        assert_eq!(surface, 64);
     }
 
     #[test]
-    fn part2() {}
+    fn part2() {
+        let cubes = parse(CUBES);
+        let (surface, obsidian) = surface(&cubes);
+        assert_eq!(surface_without_trapped_air(surface, obsidian), 58);
+    }
 }

diff --git a/src/days.rs b/src/days.rs
index 2dc6343..28f5a5a 100644 (file)
--- a/src/days.rs
+++ b/src/days.rs
@@ -181,5 +181,10 @@ pub fn day17() -> String {
 
 pub fn day18() -> String {
     let cubes = day18::parse(&fs::read_to_string("data/day18.input").unwrap());
-    format!("part1: {}, part2: {}", day18::surface(&cubes), 0)
+    let (surface, obsidian) = day18::surface(&cubes);
+    format!(
+        "part1: {}, part2: {}",
+        surface,
+        day18::surface_without_trapped_air(surface, obsidian)
+    )
 }