feat: solve day 15 part 2

src/day11.rs

@@ -12,7 +12,7 @@ pub fn parse_input(input: &str) -> [[u32; 10]; 10] {
         .unwrap()
 }
 
-fn display_grid(grid: &[[u32; 10]; 10]) {
+fn _display_grid(grid: &[[u32; 10]; 10]) {
     for i in 0..grid.len() {
         for j in 0..grid[i].len() {
             print!("{:X}", grid[i][j]);

src/day15.rs

@@ -6,7 +6,36 @@ use priority_queue::PriorityQueue;
 pub struct Grid {
     rows: u32,
     cols: u32,
-    data: Vec<u32>
+    data: Vec<u32>,
+    scale: u32
+}
+
+impl Grid {
+    fn new(rows: u32, cols: u32, data: Vec<u32>) -> Grid {
+        return Grid {
+            rows, cols, data,
+            scale: 1
+        }
+    }
+
+    fn get(&self, point: &(u32, u32)) -> u32 {
+        let row = point.0 % self.rows;
+        let col = point.1 % self.cols;
+        let value = self.data[(row * self.cols + col) as usize];
+        return (value + point.0 / self.rows + point.1 / self.cols - 1) % 9 + 1;
+    }
+
+    fn width(&self) -> u32 {
+        self.cols * self.scale
+    }
+
+    fn height(&self) -> u32 {
+        self.rows * self.scale
+    }
+
+    fn within_bounds(&self, point: &(i32, i32)) -> bool {
+        point.0 >= 0 && point.1 >= 0 && point.0 < self.height() as i32 && point.1 < self.width() as i32
+    }
 }
 
 pub fn parse_input(input: &str) -> Grid {
@@ -20,19 +49,26 @@ pub fn parse_input(input: &str) -> Grid {
             data.push(c.to_digit(10).unwrap());
         }
     }
-    return Grid { rows, cols, data };
+    return Grid::new(rows, cols, data);
+}
+
+fn find_neighbours(pos: &(u32, u32), grid: &Grid, offsets: &[(i32, i32)]) -> Vec<(u32, u32)> {
+    let mut neighbours = Vec::new();
+    for offset in offsets {
+        let row = pos.0 as i32 + offset.0;
+        let col = pos.1 as i32 + offset.1;
+        if grid.within_bounds(&(row, col)) {
+            neighbours.push((row as u32, col as u32));
+        }
+    }
+    return neighbours;
 }
 
 fn find_shortest_path_cost(grid: &Grid) -> u32 {
     let mut total_costs: HashMap<(u32, u32), u32> = HashMap::new();
     let mut min_pq: PriorityQueue<(u32, u32), i32> = PriorityQueue::new();
     let mut visited: HashSet<(u32, u32)> = HashSet::new();
-    let neighbour_offsets = [
-        (0, 1),
-        (0, -1),
-        (1, 0),
-        (-1, 0)
-    ];
+    let neighbour_offsets = [ (0, 1), (0, -1), (1, 0), (-1, 0) ];
     min_pq.push((0, 0), 0);
     total_costs.insert((0, 0), 0);
 
@@ -40,19 +76,12 @@ fn find_shortest_path_cost(grid: &Grid) -> u32 {
         let new_smallest = min_pq.pop().unwrap().0;
         visited.insert(new_smallest);
 
-        for offset in neighbour_offsets {
-            let neighbour_row = new_smallest.0 as i32 + offset.0;
-            let neighbour_col = new_smallest.1 as i32 + offset.1;
-            if !(neighbour_row >= 0 && neighbour_col >= 0 && neighbour_row < grid.rows as i32 && neighbour_col < grid.cols as i32) {
-                continue;
-            }
-            let neighbour = (neighbour_row as u32, neighbour_col as u32);
-
+        for neighbour in find_neighbours(&new_smallest, grid, &neighbour_offsets) {
             if visited.contains(&neighbour) {
                 continue;
             }
 
-            let alt_distance = grid.data[(neighbour_row as u32 * grid.cols + neighbour_col as u32) as usize];
+            let alt_distance = grid.get(&neighbour);
             let alt_path = total_costs.get(&new_smallest).unwrap_or(&u32::MAX) + alt_distance;
             if alt_path < *total_costs.get(&neighbour).unwrap_or(&u32::MAX) {
                 total_costs.insert(neighbour, alt_path);
@@ -61,13 +90,18 @@ fn find_shortest_path_cost(grid: &Grid) -> u32 {
         }
     }
     
-    return *total_costs.get(&(grid.rows-1, grid.cols-1)).unwrap();
+    return *total_costs.get(&(grid.height()-1, grid.width()-1)).unwrap();
 }
 
 pub fn part1(grid: &Grid) -> u32 {
     find_shortest_path_cost(grid)
 }
 
+pub fn part2(grid: &mut Grid) -> u32 {
+    grid.scale = 5;
+    find_shortest_path_cost(grid)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -87,4 +121,21 @@ mod tests {
         let result = part1(&grid);
         assert_eq!(result, 40);
     }
+
+    #[test]
+    fn part2_example() {
+        let mut grid = parse_input("1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581");
+        let result = part2(&mut grid);
+        assert_eq!(result, 315);
+    }
 }
+

src/main.rs

@@ -58,6 +58,7 @@ fn run(day: i32, part: i32, input_filename: &str) {
         "14.1" => println!("{}", day14::part1(&day14::parse_input(&contents))),
         "14.2" => println!("{}", day14::part2(&day14::parse_input(&contents))),
         "15.1" => println!("{}", day15::part1(&day15::parse_input(&contents))),
+        "15.2" => println!("{}", day15::part2(&mut day15::parse_input(&contents))),
         _ => println!("Day {} part {} not found", day, part)
     }
 }