diff --git a/src/holt59/aoc/2021/day11.py b/src/holt59/aoc/2021/day11.py
index 07e201e..d987fd7 100644
--- a/src/holt59/aoc/2021/day11.py
+++ b/src/holt59/aoc/2021/day11.py
@@ -1,7 +1,66 @@
+import itertools as it
 from typing import Any, Iterator
 
 from ..base import BaseSolver
 
 
+def do_step(values: list[list[int]]) -> tuple[list[list[int]], set[tuple[int, int]]]:
+    values = [[c + 1 for c in r] for r in values]
+    flashed: set[tuple[int, int]] = set()
+
+    while True:
+        found = False
+
+        for i_row, row in enumerate(values):
+            for i_col, col in enumerate(row):
+                if col <= 9 or (i_row, i_col) in flashed:
+                    continue
+
+                found = True
+                flashed.add((i_row, i_col))
+                for dr, dc in it.product((-1, 0, 1), repeat=2):
+                    if 0 <= i_row + dr < len(values) and 0 <= i_col + dc < len(
+                        values[0]
+                    ):
+                        values[i_row + dr][i_col + dc] += 1
+
+        if not found:
+            break
+
+    for i, j in flashed:
+        values[i][j] = 0
+
+    return values, flashed
+
+
 class Solver(BaseSolver):
-    def solve(self, input: str) -> Iterator[Any]: ...
+    def print_grid(self, values: list[list[int]], flashed: set[tuple[int, int]]):
+        for i_row, row in enumerate(values):
+            s_row = ""
+            for i_col, col in enumerate(row):
+                if (i_row, i_col) in flashed:
+                    s_row += f"\033[0;31m{col}\033[0;00m"
+                else:
+                    s_row += str(col)
+            self.logger.info(s_row)
+        self.logger.info("")
+
+    def solve(self, input: str) -> Iterator[Any]:
+        values_0 = [[int(c) for c in r] for r in input.splitlines()]
+
+        values = values_0
+        total_flashed: int = 0
+        for _ in range(100):
+            values, flashed = do_step(values)
+            total_flashed += len(flashed)
+
+        yield total_flashed
+
+        n_cells = len(values) * len(values[0])
+        flashed: set[tuple[int, int]] = set()
+        values, step = values_0, 0
+        while len(flashed) != n_cells:
+            values, flashed = do_step(values)
+            step += 1
+
+        yield step
diff --git a/src/holt59/aoc/inputs/holt59/2021/day11.txt b/src/holt59/aoc/inputs/holt59/2021/day11.txt
index e69de29..e462b30 100644
--- a/src/holt59/aoc/inputs/holt59/2021/day11.txt
+++ b/src/holt59/aoc/inputs/holt59/2021/day11.txt
@@ -0,0 +1,10 @@
+4738615556
+6744423741
+2812868827
+8844365624
+4546674266
+4518674278
+7457237431
+4524873247
+3153341314
+3721414667
diff --git a/src/holt59/aoc/inputs/tests/2021/day11.txt b/src/holt59/aoc/inputs/tests/2021/day11.txt
index e69de29..03743f6 100644
--- a/src/holt59/aoc/inputs/tests/2021/day11.txt
+++ b/src/holt59/aoc/inputs/tests/2021/day11.txt
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526