day 22

README.md

@@ -58,8 +58,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 19](./src/bin/19.rs) | `504.1µs` | `486.3µs` |
 | [Day 20](./src/bin/20.rs) | `4.3ms` | `18.2ms` |
 | [Day 21](./src/bin/21.rs) | `1.5ms` | `70.1ms` |
+| [Day 22](./src/bin/22.rs) | `9.5ms` | `17.6ms` |
 
-**Total: 46581.81ms**
+**Total: 46608.91ms**
 <!--- benchmarking table --->
 
 ---

src/bin/22.rs

@@ -0,0 +1,139 @@
+use std::cmp::{max, min};
+use std::collections::{VecDeque, HashSet};
+
+advent_of_code::solution!(22);
+
+struct Brick {
+    x: usize,
+    y: usize,
+    z: usize,
+    ex: usize,
+    ey: usize,
+    ez: usize
+}
+
+impl Brick {
+    fn overlap_plane(&self, other: &Brick) -> bool {
+        max(self.x, other.x) <= min(self.ex, other.ex) &&  // Overlap in x
+            max(self.y, other.y) <= min(self.ey, other.ey) // Overlap in y
+    }
+}
+
+fn parse(input: &str) -> Vec<Brick> {
+    input.lines()
+         .map(|l| {
+             let parts: Vec<usize> = l.split(&[',', '~']).map(|c| c.parse().unwrap()).collect();
+
+             Brick { x: parts[0],
+                     y: parts[1],
+                     z: parts[2],
+                     ex: parts[3],
+                     ey: parts[4],
+                     ez: parts[5]
+             }
+         })
+         .collect()
+}
+
+fn fall_bricks(bricks: &mut Vec<Brick>) {
+    bricks.sort_by_key(|b| b.z);
+
+    for i in 0..bricks.len() {
+        let mut top_z: usize = 1;
+
+        let bricks_below: &[Brick] = &bricks[..i];
+
+        for b in bricks_below {
+            if bricks[i].overlap_plane(b) {
+                top_z = max(top_z, b.ez + 1);
+            }
+        }
+
+        let brick = &mut bricks[i];
+
+        brick.ez -= brick.z - top_z;
+        brick.z = top_z;
+    }
+
+    bricks.sort_by_key(|b| b.z);
+}
+
+fn compute_supports(bricks: &Vec<Brick>) -> (Vec<Vec<usize>>, Vec<Vec<usize>>) {
+    let mut supported_by: Vec<Vec<usize>> = vec![vec![]; bricks.len()];
+    let mut supports: Vec<Vec<usize>> = vec![vec![]; bricks.len()];
+
+    for (j, brick) in bricks.iter().enumerate() {
+        for (i, below) in bricks[..j].iter().enumerate() {
+            if brick.overlap_plane(below) && brick.z == below.ez + 1 {
+                supported_by[j].push(i);
+                supports[i].push(j);
+            }
+        }
+    }
+
+    (supported_by, supports)
+}
+
+fn compute_falls(brick: usize, supported_by: &Vec<Vec<usize>>, supports: &Vec<Vec<usize>>) -> u32 {
+    let will_fall: Vec<usize> = supports[brick].iter().filter(|&b| supported_by[*b].len() == 1).cloned().collect();
+    let mut queue = VecDeque::from_iter(will_fall.iter().cloned());
+
+    let mut falling: HashSet<usize> = HashSet::from_iter(will_fall.into_iter());
+    falling.insert(brick);
+
+    while let Some(other) = queue.pop_front() {
+        for &b in &supports[other] {
+            if !falling.contains(&b) {
+                if supported_by[b].iter().all(|s| falling.contains(s)) {
+                    queue.push_back(b);
+                    falling.insert(b);
+                }
+            }
+        }
+    }
+
+    (falling.len() - 1) as u32
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let mut bricks = parse(input);
+    fall_bricks(&mut bricks);
+
+    let (supported_by, supports) = compute_supports(&bricks);
+
+    let result: usize = supports.iter()
+                                .filter(|bricks|
+                                        bricks.iter().all(|&i| supported_by[i].len() >= 2))
+                                .count();
+
+    Some(result as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let mut bricks = parse(input);
+    fall_bricks(&mut bricks);
+
+    let (supported_by, supports) = compute_supports(&bricks);
+
+    (0..bricks.len())
+        .map(|i| compute_falls(i, &supported_by, &supports))
+        .sum::<u32>()
+        .into()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(5));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(7));
+    }
+}