day14

1 files changed, 132 insertions, 0 deletions

diff --git a/src/bin/day14.rs b/src/bin/day14.rs
new file mode 100644
index 0000000..c6323a3
--- /dev/null
+++ b/src/bin/day14.rs
@@ -0,0 +1,132 @@
+use std::collections::HashMap;
+
+static DAY: u8 = 14;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", sand_before_abyss(&input));
+    println!("{DAY}b: {}", sand_to_rest(&input));
+}
+
+#[derive(Debug)]
+enum Material {
+    Rock,
+    Sand,
+}
+
+fn parse_map(input: &[String]) -> HashMap<(isize,isize),Material> {
+    let mut map = HashMap::new();
+
+    for line in input {
+        let mut path = Vec::new();
+        for coord in line.split(" -> ") {
+            let (x,y) = coord.split_once(',').expect("coordinate needs to contain ,");
+            let x = x.parse::<isize>().expect("x coord should be number");
+            let y = y.parse::<isize>().expect("y coord should be number");
+            path.push((x,y));
+        }
+        for pos in path.windows(2) {
+            let (x1, x2) = if pos[0].0 < pos[1].0 {
+                (pos[0].0, pos[1].0)
+            } else {
+                (pos[1].0, pos[0].0)
+            };
+
+            let (y1, y2) = if pos[0].1 < pos[1].1 {
+                (pos[0].1, pos[1].1)
+            } else {
+                (pos[1].1, pos[0].1)
+            };
+
+            for x in x1 ..= x2 {
+                for y in y1 ..= y2 {
+                    map.insert((x,y), Material::Rock);
+                }
+            }
+        }
+    }
+    map
+}
+
+fn next_sand_pos(map: &mut HashMap<(isize,isize),Material>, pos: (isize,isize)) -> Option<(isize,isize)> {
+    let next_positions = [
+        (pos.0, pos.1 + 1),
+        (pos.0 - 1, pos.1 + 1),
+        (pos.0 + 1, pos.1 + 1),
+    ];
+    next_positions.iter().find(|next_pos| !map.contains_key(next_pos)).copied()
+}
+
+fn sand_above_abyss(map: &mut HashMap<(isize,isize),Material>, above: isize) -> bool {
+    let mut pos = (500,0);
+
+    while pos.1 <= above {
+        match next_sand_pos(map, pos) {
+            Some(next_pos) => pos = next_pos,
+            None => {
+                map.insert(pos, Material::Sand);
+                break;
+            }
+        }
+    }
+
+    pos.1 <= above
+}
+
+fn sand_at_source(map: &mut HashMap<(isize,isize),Material>, floor: isize) -> bool {
+    let mut pos = (500,0);
+
+    loop {
+        match next_sand_pos(map, pos) {
+            Some(next_pos) => {
+                if next_pos.1 == floor {
+                    map.insert(pos, Material::Sand);
+                    break;
+                }
+                pos = next_pos;
+            },
+            None => {
+                map.insert(pos, Material::Sand);
+                break;
+            }
+        }
+    }
+
+    pos == (500,0)
+}
+
+fn sand_before_abyss(input: &[String]) -> usize {
+    let mut map = parse_map(input);
+    let lowest_rock = *map.keys().max_by_key(|(_,y)| y).expect("map should have a rock");
+    let mut sand = 0;
+    while sand_above_abyss(&mut map, lowest_rock.1) {
+        sand += 1;
+    }
+    sand
+}
+
+fn sand_to_rest(input: &[String]) -> usize {
+    let mut map = parse_map(input);
+    let floor = map.keys().max_by_key(|(_,y)| y).expect("map should have a rock").1 + 2;
+    let mut sand = 0;
+    while !sand_at_source(&mut map, floor) {
+        sand += 1;
+    }
+    sand + 1
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "498,4 -> 498,6 -> 496,6",
+            "503,4 -> 502,4 -> 502,9 -> 494,9",
+        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
+
+        assert_eq!(sand_before_abyss(&input), 24);
+        assert_eq!(sand_to_rest(&input), 93);
+    }
+}