Slow implementation for day 15

2021/src/day14.rs

@@ -103,7 +103,6 @@ pub fn part2(input: &mut dyn Read) -> String {
     parts_common(input, 40)
 }
 
-#[cfg(test)]
 #[cfg(test)]
 mod tests {
     use super::*;

2021/src/day15.rs

@@ -1,9 +1,163 @@
+use std::cmp::Reverse;
+use std::collections::BinaryHeap;
 use std::io::Read;
 
-pub fn part1(_input: &mut dyn Read) -> String {
-    todo!()
+use crate::common::LineIter;
+
+type Point = (i32, i32);
+
+struct Map {
+    width: usize,
+    data: Vec<u8>,
 }
 
-pub fn part2(_input: &mut dyn Read) -> String {
-    todo!()
+impl Map {
+    pub fn from_input(input: &mut dyn Read) -> Self {
+        let mut reader = LineIter::new(input);
+
+        let mut data = reader.next().unwrap().as_bytes().to_owned();
+        let width = data.len();
+
+        while let Some(line) = reader.next() {
+            let line = line.as_bytes();
+            debug_assert_eq!(line.len(), width);
+
+            data.extend_from_slice(line);
+        }
+
+        data.iter_mut().for_each(|b| *b -= b'0');
+
+        Self { width, data }
+    }
+
+    pub fn from_input2(input: &mut dyn Read) -> Self {
+        let mut reader = LineIter::new(input);
+
+        let mut lines = Vec::new();
+
+        while let Some(line) = reader.next() {
+            let mut line = line.as_bytes().to_owned();
+            line.iter_mut().for_each(|b| *b -= b'0');
+            lines.push(line);
+        }
+
+        let mut data = Vec::new();
+        let width = lines[0].len();
+
+        for _y_repeat in 0..5 {
+            for line in &mut lines {
+                data.extend_from_slice(line);
+
+                for _ in 0..4 {
+                    let starting_pos = data.len() - width;
+                    data.extend_from_within(starting_pos..);
+                    let starting_pos = data.len() - width;
+                    data[starting_pos..]
+                        .iter_mut()
+                        .for_each(|b| *b = (*b % 9) + 1);
+                }
+
+                line.iter_mut().for_each(|b| *b = (*b % 9) + 1);
+            }
+        }
+
+        Self {
+            width: width * 5,
+            data,
+        }
+    }
+
+    pub fn shortest_path(&self, start: Point, end: Point) -> u32 {
+        let mut todo = BinaryHeap::new();
+        todo.push(Reverse((Self::manhattan(start, end), 0, start)));
+
+        let mut visited = vec![false; self.data.len()];
+
+        let height = self.height() as i32;
+
+        while let Some(Reverse((_, distance, pos))) = todo.pop() {
+            if pos == end {
+                return distance;
+            }
+
+            if visited[self.index(pos)] {
+                continue;
+            }
+
+            visited[self.index(pos)] = true;
+
+            let (x, y) = pos;
+
+            for dy in -1..=1 {
+                if y + dy < 0 || y + dy >= height {
+                    continue;
+                }
+
+                for dx in -1..=1 {
+                    if x + dx < 0 || (x + dx) >= self.width as i32 || dx * dy != 0 {
+                        continue;
+                    }
+
+                    let new = (x + dx, y + dy);
+                    let index = self.index(new);
+
+                    if visited[index] {
+                        continue;
+                    }
+
+                    let new_distance = distance + self.data[index] as u32;
+                    let new_guess = Self::manhattan(new, end) + new_distance;
+
+                    todo.push(Reverse((new_guess, new_distance, new)));
+                }
+            }
+        }
+
+        panic!("No route found from {:?} to {:?}", start, end);
+    }
+
+    fn manhattan((xa, ya): Point, (xb, yb): Point) -> u32 {
+        (xa - xb).abs() as u32 + (ya - yb).abs() as u32
+    }
+
+    pub fn height(&self) -> usize {
+        self.data.len() / self.width
+    }
+
+    pub fn index(&self, (x, y): Point) -> usize {
+        y as usize * self.width + x as usize
+    }
+}
+
+pub fn part1(input: &mut dyn Read) -> String {
+    let map = Map::from_input(input);
+
+    map.shortest_path((0, 0), (map.width as i32 - 1, map.height() as i32 - 1))
+        .to_string()
+}
+
+pub fn part2(input: &mut dyn Read) -> String {
+    let map = Map::from_input2(input);
+
+    map.shortest_path((0, 0), (map.width as i32 - 1, map.height() as i32 - 1))
+        .to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::test_implementation;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/15.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation(part1, SAMPLE, 40);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation(part2, SAMPLE, 315);
+    }
 }

2021/src/samples/15.txt

@@ -0,0 +1,10 @@
+1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581