diff --git a/projects/aoc/src/year2021/Solutions2021.kiss b/projects/aoc/src/year2021/Solutions2021.kiss
index 2d701205..fc0aa5d2 100644
--- a/projects/aoc/src/year2021/Solutions2021.kiss
+++ b/projects/aoc/src/year2021/Solutions2021.kiss
@@ -69,7 +69,12 @@
         (assert (= 462693 (apply + (map (map (Util.readLines "src/year2021/inputs/day10.txt") getLineType) score))))
         (let [completionScores (sort (filter (map (map (Util.readLines "src/year2021/inputs/day10.txt") getLineType) completionScore)))]
             (assert (= 3094671161 (nth completionScores (Math.floor (/ completionScores.length 2)))))))
-    (dayTodo 11)
+    (day 11
+        (load "day11.kiss")
+        (assert (= 35 (flashesAfter 2 "src/year2021/inputs/day11-example.txt")))
+        (assert (= 1656 (flashesAfter 100 "src/year2021/inputs/day11-example.txt")))
+        (assert (= 1723 (flashesAfter 100 "src/year2021/inputs/day11.txt")))
+        ~(firstSimultaneousFlash "src/year2021/inputs/day11.txt"))
     (day 12
         (load "day12.kiss")
         (assert (= 10 .length (allPaths "start" "end" "src/year2021/inputs/day12-example.txt")))
diff --git a/projects/aoc/src/year2021/day11.kiss b/projects/aoc/src/year2021/day11.kiss
new file mode 100644
index 00000000..460c09e6
--- /dev/null
+++ b/projects/aoc/src/year2021/day11.kiss
@@ -0,0 +1,52 @@
+(function readGrid [file]
+    (for line (Util.readLines file) (map (line.split "") Std.parseInt)))
+
+(function :Array<Array<Int>> neighboringPoints [:Array<Int> point]
+    (let [[col row] point]
+        (apply concat (for c (range (- col 1) (+ col 2))
+            (for r (range (- row 1) (+ row 2)) [c r])))))
+
+// Return true if any new flashes were triggered, so handleFlashes can be called again
+(function :Bool handleFlashes [:Array<Array<Int>> grid]
+    (let [&mut newFlash false]
+        (doFor row (range grid.length)
+            (doFor col (range .length (first grid))
+                (when (<= 10 (nth (nth grid row) col))
+                    (set newFlash true)
+                    (setNth (nth grid row) col 0)
+                    (doFor [c r] (neighboringPoints [col row])
+                        (when (and
+                                    (< c .length (first grid))
+                                    (>= c 0)
+                                    (< r grid.length)
+                                    (>= r 0)
+                                    !(= 0 (nth (nth grid r) c)))
+                            (setNth (nth grid r) c (+ 1 (nth (nth grid r) c))))))))
+        newFlash))
+
+(function _stepGrid [:Array<Array<Int>> grid]
+    (let [newGrid
+                (for line grid (for octo line (+ octo 1)))]
+        (while (handleFlashes newGrid) 0)
+        newGrid))
+(var stepGrid (memoize _stepGrid))
+
+(function _flashes [:Array<Array<Int>> grid]
+    (apply + (for line grid (count line ->num ?(= num 0)))))
+(var flashes (memoize _flashes))
+
+(function flashesAfter [steps file]
+    (let [&mut grid (readGrid file)
+            &mut :Float f 0]
+        (doFor i (range steps)
+            (set grid (stepGrid grid))
+            (+= f (flashes grid)))
+        f))
+
+(function firstSimultaneousFlash [file]
+    (let [&mut grid (readGrid file)
+            &mut step 0]
+        (until (= (* grid.length .length (nth grid 0)) (flashes grid))
+            (set grid (stepGrid grid))
+            (+= step 1))
+        step))
\ No newline at end of file
diff --git a/projects/aoc/src/year2021/inputs/day11-example.txt b/projects/aoc/src/year2021/inputs/day11-example.txt
new file mode 100644
index 00000000..a3819c90
--- /dev/null
+++ b/projects/aoc/src/year2021/inputs/day11-example.txt
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
\ No newline at end of file
diff --git a/projects/aoc/src/year2021/inputs/day11.txt b/projects/aoc/src/year2021/inputs/day11.txt
new file mode 100644
index 00000000..b5a77cd8
--- /dev/null
+++ b/projects/aoc/src/year2021/inputs/day11.txt
@@ -0,0 +1,10 @@
+2238518614
+4552388553
+2562121143
+2666685337
+7575518784
+3572534871
+8411718283
+7742668385
+1235133231
+2546165345