Down to 65 μs from 80 μs (average on 1000 runs)

diff --git a/src/day10.rs b/src/day10.rs
index 43dd221..ca7c7f6 100644 (file)
--- a/src/day10.rs
+++ b/src/day10.rs
@@ -2,30 +2,30 @@ use std::io::BufRead;
 
 use nalgebra::DMatrix;
 
-type Map = DMatrix<u32>;
+type Map = DMatrix<u8>;
 type Position = (usize, usize);
 
 pub fn read_map(reader: &mut dyn BufRead) -> (Map, Vec<Position>) {
-    let mut map = Map::default();
     let mut start_positions: Vec<Position> = Vec::new();
 
+    let mut data: Vec<u8> = Vec::new();
+    let mut nb_rows = 0;
+
     for (i, l) in reader.lines().enumerate() {
-        if map.nrows() < i + 1 {
-            map = map.insert_row(i, 0);
-        }
+        nb_rows += 1;
         for (j, c) in l.unwrap().chars().enumerate() {
-            if map.ncols() < j + 1 {
-                map = map.insert_column(j, 0);
-            }
-            let level = c.to_digit(10).unwrap();
-            map[(i, j)] = level;
+            let level = c.to_digit(10).unwrap() as u8;
+            data.push(level);
             if level == 0 {
                 start_positions.push((i, j));
             }
         }
     }
 
-    (map, start_positions)
+    (
+        Map::from_row_slice(nb_rows, data.len() / nb_rows, &data),
+        start_positions,
+    )
 }
 
 pub fn score(map: &Map, start_positions: &[Position], multiple_paths: bool) -> u32 {