day(22): add solution

Signed-off-by: Matej Focko <me@mfocko.xyz>

samples/day22.txt

@@ -0,0 +1,7 @@
+1,0,1~1,2,1
+0,0,2~2,0,2
+0,2,3~2,2,3
+0,0,4~0,2,4
+2,0,5~2,2,5
+0,1,6~2,1,6
+1,1,8~1,1,9

src/bin/day22.rs

@@ -0,0 +1,109 @@
+use std::collections::HashMap;
+
+use aoc_2023::*;
+
+type Output1 = usize;
+type Output2 = Output1;
+
+type Coord2D = Vector2D<i32>;
+type Coord = Vector3D<i32>;
+
+#[derive(Debug, Clone, Copy)]
+struct Brick {
+    min: Coord,
+    max: Coord,
+}
+
+impl Brick {
+    fn new(min: Coord, max: Coord) -> Self {
+        Self { min, max }
+    }
+}
+
+struct Day22 {
+    bricks: Vec<Brick>,
+    falls: Vec<usize>,
+}
+
+impl Day22 {
+    fn fall(bricks: &mut [Brick]) -> usize {
+        let mut top = HashMap::<Coord2D, i32>::new();
+        let mut count = 0;
+
+        for b in bricks {
+            let mut fall = b.min.z();
+            for x in b.min.x()..=b.max.x() {
+                for y in b.min.y()..=b.max.y() {
+                    fall = fall.min(b.min.z() - top.get(&Coord2D::new(x, y)).unwrap_or(&0) - 1);
+                }
+            }
+
+            if fall > 0 {
+                count += 1;
+            }
+
+            b.min -= Coord::new(0, 0, fall);
+            b.max -= Coord::new(0, 0, fall);
+
+            for x in b.min.x()..=b.max.x() {
+                for y in b.min.y()..=b.max.y() {
+                    top.insert(Coord2D::new(x, y), b.max.z());
+                }
+            }
+        }
+
+        count
+    }
+
+    fn compute(&mut self) {
+        if !self.falls.is_empty() {
+            // already been computed
+            return;
+        }
+
+        // sort them for the solving
+        self.bricks.sort_by_key(|b| b.min.z());
+
+        Self::fall(&mut self.bricks);
+        self.falls = (0..self.bricks.len())
+            .map(|i| Self::fall(&mut [&self.bricks[0..i], &self.bricks[i + 1..]].concat()))
+            .collect_vec();
+    }
+}
+
+impl Solution<Output1, Output2> for Day22 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        let lines: Vec<String> = file_to_lines(pathname);
+
+        let mut bricks = vec![];
+        for (x0, y0, z0, x1, y1, z1) in lines.iter().map(|l| {
+            l.split(&[',', '~'])
+                .map(|c| c.parse::<i32>().unwrap())
+                .collect_tuple()
+                .unwrap()
+        }) {
+            bricks.push(Brick::new(Coord::new(x0, y0, z0), Coord::new(x1, y1, z1)));
+        }
+
+        Self {
+            bricks,
+            falls: vec![],
+        }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        self.compute();
+        self.falls.iter().filter(|b| **b == 0).count()
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        self.compute();
+        self.falls.iter().sum::<usize>()
+    }
+}
+
+fn main() -> Result<()> {
+    Day22::main()
+}
+
+test_sample!(day_22, Day22, 5, 7);