day22

src/day22.rs

@@ -0,0 +1,133 @@
+use std::collections::VecDeque;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+use regex::Regex;
+
+pub struct Brick {
+    up: Vec<Vec<usize>>,
+    down: Vec<Vec<usize>>,
+}
+
+
+#[aoc_generator(day22)]
+fn parse(input: &str) -> Brick {
+    let re: Regex = Regex::new(r"\d+").unwrap();
+
+    let mut bricks: Vec<[usize; 6]> = input.lines().map(|line| {
+        re.captures_iter(line)
+            .map(|c| c.extract::<0>().0.parse::<usize>().unwrap())
+            .collect::<Vec<_>>().try_into().unwrap()
+    }).collect::<Vec<_>>();
+
+    let mut heights = [[0; 10]; 10];
+    let mut indices = [[usize::MAX; 10]; 10];
+    let mut up = vec![Vec::new(); bricks.len()];
+    let mut down = vec![Vec::new(); bricks.len()];
+
+    bricks.sort_unstable_by_key(|b| b[2]);
+
+    for (i, &[x1, y1, z1, x2, y2, z2]) in bricks.iter().enumerate() {
+        let height = z2 - z1 + 1;
+        let mut top = 0;
+        let mut previous = usize::MAX;
+
+        for x in x1..=x2 {
+            for y in y1..=y2 {
+                top = top.max(heights[x][y]);
+            }
+        }
+
+        for x in x1..=x2 {
+            for y in y1..=y2 {
+                if heights[x][y] == top {
+                    let index = indices[x][y];
+                    if index != previous {
+                        up[index].push(i);
+                        down[i].push(index);
+                        previous = index;
+                    }
+                }
+
+                heights[x][y] = top + height;
+                indices[x][y] = i;
+            }
+        }
+    }
+
+    Brick { up , down }
+}
+
+#[aoc(day22, part1)]
+fn part1(input: &Brick) -> usize {
+    let Brick { down, .. } = input;
+    let mut safe = vec![true; down.len()];
+
+    for underneath in down {
+        if underneath.len() == 1 {
+            safe[underneath[0]] = false;
+        }
+    }
+
+    safe.iter().filter(|&&b| b).count()
+}
+
+#[aoc(day22, part2)]
+fn part2(input: &Brick) -> usize {
+    let Brick { up, down } = input;
+    let mut safe = vec![true; down.len()];
+
+    for underneath in down {
+        if underneath.len() == 1 {
+            safe[underneath[0]] = false;
+        }
+    }
+
+    let mut result = 0;
+    let mut todo = VecDeque::new();
+    let mut removed = vec![usize::MAX; down.len()];
+
+    for (start, &safe) in safe.iter().enumerate() {
+        if safe {
+            continue;
+        }
+
+        todo.push_back(start);
+        removed[start] = start;
+
+        while let Some(current) = todo.pop_front() {
+            for &next in &up[current] {
+                if removed[next] != start && down[next].iter().all(|&i| removed[i] == start) {
+                    result += 1;
+                    removed[next] = start;
+                    todo.push_back(next);
+                }
+            }
+        }
+    }
+
+    result
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+const EX: &str = r"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";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 5);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EX)), 7);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day22;
 mod day21;
 mod day20;
 mod day19;