diff --git a/11/input.txt b/11/input.txt
new file mode 100644
index 0000000..7fbfb71
--- /dev/null
+++ b/11/input.txt
@@ -0,0 +1,10 @@
+4472562264
+8631517827
+7232144146
+2447163824
+1235272671
+5133527146
+6511372417
+3841841614
+8621368782
+3246336677
\ No newline at end of file
diff --git a/11/main.go b/11/main.go
new file mode 100644
index 0000000..fb56022
--- /dev/null
+++ b/11/main.go
@@ -0,0 +1,120 @@
+package main
+
+import (
+	"log"
+	"math"
+	"os"
+	"strings"
+)
+
+func main() {
+	inputBytes, _ := os.ReadFile("input.txt")
+	input := strings.Split(string(inputBytes), "\n")
+
+	log.Println("Puzzle 1:", puzzle1(input))
+	log.Println("Puzzle 2:", puzzle2(input))
+}
+
+func puzzle1(input []string) int {
+	// Read input into grid
+	grid := readInput(input)
+	totalFlashes := 0
+	// 100 steps
+	for step := 1; step <= 100; step++ {
+		// Increase every energy level (every cell) by 1
+		for i := range grid {
+			for j := range grid[i] {
+				grid[i][j]++
+			}
+		}
+		// Flash cells
+		for i := range grid {
+			for j := range grid[i] {
+				if grid[i][j] > 9 {
+					totalFlashes += flash(grid, j, i)
+				}
+			}
+		}
+	}
+	return totalFlashes
+}
+
+func puzzle2(input []string) int {
+	// Read input into grid
+	grid := readInput(input)
+	totalFlashes := 0
+forsteps:
+	for step := 1; step < math.MaxInt; step++ {
+		// Increase every energy level (every cell) by 1
+		for i := range grid {
+			for j := range grid[i] {
+				grid[i][j]++
+			}
+		}
+		// Flash cells
+		for i := range grid {
+			for j := range grid[i] {
+				if grid[i][j] > 9 {
+					totalFlashes += flash(grid, j, i)
+				}
+			}
+		}
+		// Check if all cells are now 0
+		for i := range grid {
+			for j := range grid[i] {
+				if grid[j][i] != 0 {
+					continue forsteps
+				}
+			}
+		}
+		// Return step
+		return step
+	}
+	return totalFlashes
+}
+
+func readInput(input []string) [][]int {
+	// Read input into 10x10 grid
+	grid := make([][]int, 10)
+	for i := range grid {
+		grid[i] = make([]int, 10)
+	}
+	for i, line := range input {
+		for j, c := range line {
+			grid[i][j] = int(c - '0')
+		}
+	}
+	return grid
+}
+
+func flash(grid [][]int, x, y int) int {
+	grid[y][x] = 0
+	flashes := 1
+	// Iterate over all adjacent cells
+	ax, ay := adjacent(x, y)
+	for i := range ax {
+		if grid[ay[i]][ax[i]] == 0 {
+			// Already flashed
+			continue
+		}
+		// Increase energy level by 1
+		grid[ay[i]][ax[i]]++
+		if grid[ay[i]][ax[i]] > 9 {
+			// Flash cell aswell
+			flashes += flash(grid, ax[i], ay[i])
+		}
+	}
+	return flashes
+}
+
+func adjacent(x, y int) (xs, ys []int) {
+	for i := 0; i < 10; i++ {
+		for j := 0; j < 10; j++ {
+			if i >= 0 && i <= 9 && i >= x-1 && i <= x+1 && j >= 0 && j <= 9 && j >= y-1 && j <= y+1 && !(i == x && j == y) {
+				xs = append(xs, i)
+				ys = append(ys, j)
+			}
+		}
+	}
+	return
+}
diff --git a/11/main_test.go b/11/main_test.go
new file mode 100644
index 0000000..4d0eda7
--- /dev/null
+++ b/11/main_test.go
@@ -0,0 +1,17 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test(t *testing.T) {
+	inputBytes, _ := os.ReadFile("test.txt")
+	input := strings.Split(string(inputBytes), "\n")
+
+	assert.Equal(t, 1656, puzzle1(input))
+	assert.Equal(t, 195, puzzle2(input))
+}
diff --git a/11/test.txt b/11/test.txt
new file mode 100644
index 0000000..a3819c9
--- /dev/null
+++ b/11/test.txt
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
\ No newline at end of file