day17

src/day17.rs

@@ -0,0 +1,115 @@
+use std::{collections::BinaryHeap, cmp::Reverse};
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[derive(Debug)]
+struct Grid {
+    data: Box<[u8]>,
+    offset: usize
+}
+
+impl Grid {
+    fn from_str(s: &str) -> Self {
+        let mut lines = s.lines().peekable();
+        let line_len = lines.peek().map_or(0, |line| line.len());
+        Self {
+            data: lines.flat_map(str::as_bytes).map(|&char| char - b'0').collect::<Box<_>>(),
+            offset: line_len
+        }
+    }
+
+    fn next_pos(&self, p: usize, dir: u8) -> Option<usize> {
+        Some(match dir {
+            0 if p > self.offset => p - self.offset,
+            1 if (p + 1) % self.offset != 0 => p + 1,
+            2 if p < self.data.len() - self.offset => p + self.offset,
+            3 if p % self.offset != 0 => p - 1,
+            _ => { return None }
+        })
+    }
+
+    fn run(&self, dmin: usize, dmax: usize) -> Option<usize> {
+        let lp = self.data.len() - 1;
+        let mut visit = vec![0u8; self.data.len()];
+        let mut ccache = vec![usize::MAX; 2 * self.data.len()];
+        let mut q = BinaryHeap::new();
+        q.push((Reverse(0), 0, 0));
+        q.push((Reverse(0), 0, 1));
+
+        while let Some((Reverse(cost), p, dir)) = q.pop() {
+            if p == lp {
+                return Some(cost)
+            }
+            if visit[p] & (1u8 << dir) != 0 {
+                continue;
+            }
+            visit[p] |= 1u8 << dir;
+            let odir = dir ^ 1;
+            for nd in [odir, odir ^ 2] {
+                let mut costsum = 0;
+                let mut np = p;
+                for dist in 1..=dmax {
+                    if let Some(op) = self.next_pos(np, nd) {
+                        costsum += self.data[op] as usize;
+                        if dist >= dmin {
+                            let ncost = cost + costsum;
+                            let cache_idx = (op << 1) | odir as usize;
+                            if ccache[cache_idx] > ncost {
+                                ccache[cache_idx] = ncost;
+                                q.push((Reverse(ncost), op, odir));
+                            }
+                        }
+                        np = op;
+                    }
+                }
+            }
+        }
+        None
+    }
+}
+
+
+#[aoc_generator(day17)]
+fn parse(input: &str) -> Grid {
+    Grid::from_str(input)
+}
+
+#[aoc(day17, part1)]
+fn part1(input: &Grid) -> usize {
+    input.run(1, 3).unwrap()
+}
+
+#[aoc(day17, part2)]
+fn part2(input: &Grid) -> usize {
+    input.run(4, 10).unwrap()
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EX: &str = r"2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 102);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EX)), 94);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day17;
 mod day16;
 mod day15;
 mod day14;