1 files changed, 82 insertions, 0 deletions
diff --git a/src/bin/2021/day11.rs b/src/bin/2021/day11.rs
new file mode 100644
index 0000000..fac392e
--- /dev/null
+++ b/src/bin/2021/day11.rs
@@ -0,0 +1,82 @@
+use advent_of_code::prelude::*;
+
+fn iterate(grid: &mut Grid<(u8, bool)>) -> usize {
+    let mut flashes = 0;
+    for (cell, _) in grid.cells_mut() {
+        *cell += 1;
+    }
+
+    loop {
+        let mut new_flashes = 0;
+        let mut updates: Grid<u8> = Grid::default();
+        updates.grow(grid.rows(), grid.cols());
+        for ((row, col), (cell, flashed)) in grid.indexed_cells_mut() {
+            if *flashed {
+                continue;
+            }
+            if *cell > 9 {
+                *flashed = true;
+                new_flashes += 1;
+                for (row, col) in updates.adjacent(row, col, true) {
+                    updates[row][col] += 1;
+                }
+            }
+        }
+        if new_flashes > 0 {
+            flashes += new_flashes;
+            for ((row, col), val) in updates.indexed_cells() {
+                grid[row][col].0 += val;
+            }
+        } else {
+            break;
+        }
+    }
+
+    for (cell, flashed) in grid.cells_mut() {
+        if *flashed {
+            *cell = 0;
+            *flashed = false;
+        }
+    }
+
+    flashes
+}
+
+pub fn parse(fh: File) -> Result<Grid<(u8, bool)>> {
+    Ok(parse::digit_grid(parse::raw_lines(fh))
+        .indexed_cells()
+        .map(|((row, col), cell)| ((row, col), (*cell, false)))
+        .collect())
+}
+
+pub fn part1(mut map: Grid<(u8, bool)>) -> Result<usize> {
+    let mut flashes = 0;
+    for _ in 0..100 {
+        flashes += iterate(&mut map);
+    }
+    Ok(flashes)
+}
+
+pub fn part2(mut map: Grid<(u8, bool)>) -> Result<usize> {
+    let mut step = 1;
+    loop {
+        let flashes = iterate(&mut map);
+        if flashes == (map.rows().0 * map.cols().0) {
+            break;
+        }
+        step += 1;
+    }
+    Ok(step)
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        part1(parse(parse::data(2021, 11).unwrap()).unwrap()).unwrap(),
+        1673
+    );
+    assert_eq!(
+        part2(parse(parse::data(2021, 11).unwrap()).unwrap()).unwrap(),
+        279
+    );
+}