diff --git a/functions/src/day11.ts b/functions/src/day11.ts
new file mode 100644
index 0000000..71103a6
--- /dev/null
+++ b/functions/src/day11.ts
@@ -0,0 +1,128 @@
+import Day from "./day";
+
+class Day11 implements Day {
+
+  part1(input: string[]): number | string {
+
+    const grid = OctopusGrid.parse(input);
+
+    let flashTotal = 0;
+    for (let i = 0; i < 100; i++) {
+      flashTotal += grid.runStep();
+    }
+    return flashTotal;
+  }
+
+  part2(input: string[]): number | string {
+    const grid = OctopusGrid.parse(input);
+
+    let lastFlash = 0;
+    let step = 0;
+    while(lastFlash !== 100) {
+      lastFlash = grid.runStep();
+      step++;
+    }
+    return step;
+  }
+
+}
+
+class OctopusGrid {
+  grid: number[];
+  maxX: number;
+  maxY: number;
+
+  constructor(grid: number[], width: number) {
+
+    this.grid = grid;
+    this.maxX = width;
+    this.maxY = grid.length / width;
+
+  }
+
+  static parse(input: string[]): OctopusGrid {
+
+    const grid = input.map(l => l.split("").map(s => parseInt(s)))
+      .reduce((a, b) => [...a, ...b])
+    const width = input[0].length;
+
+    return new OctopusGrid(grid, width);
+  }
+
+  runStep(): number {
+
+    // First, the energy level of each octopus increases by 1.
+    this.grid = this.grid.map(o => o + 1);
+
+    // Then, any octopus with an energy level greater than 9 flashes. This increases the energy level of all adjacent
+    // octopuses by 1, including octopuses that are diagonally adjacent. If this causes an octopus to have an energy
+    // level greater than 9, it also flashes. This process continues as long as new octopuses keep having their energy
+    // level increased beyond 9. (An octopus can only flash at most once per step.)
+    const flashGrid = Array(this.grid.length).fill(false);
+
+    for (let y = 0; y < this.maxY; y++) {
+      for (let x = 0; x < this.maxX; x++) {
+        const i = this.index(x, y);
+        const cur = this.grid[i];
+        if (cur > 9 && !flashGrid[i]) {
+          this.flash(x, y, flashGrid);
+        }
+      }
+    }
+
+    // Finally, any octopus that flashed during this step has its energy level set to 0, as it used all of its energy to flash.
+    for (let y = 0; y < this.maxY; y++) {
+      for (let x = 0; x < this.maxX; x++) {
+        const i = this.index(x, y);
+        if (flashGrid[i]) {
+          this.grid[i] = 0;
+        }
+      }
+    }
+
+    return flashGrid.filter(f => f).length;
+  }
+
+  flash(x: number, y: number, flashGrid: boolean[]) {
+
+    flashGrid[this.index(x, y)] = true;
+
+    // Charge and if needed flash all neighbors
+    for (let ny = y - 1; ny <= y + 1; ny++) {
+      for (let nx = x - 1; nx <= x + 1 ; nx++) {
+        this.chargeAndFlashIfNeeded(nx, ny, flashGrid);
+      }
+    }
+  }
+  
+  chargeAndFlashIfNeeded(x: number, y: number, flashGrid: boolean[]) {
+    // Short circuit for octopuses outside the grid
+    if (x < 0 || x >= this.maxX || y < 0 || y >= this.maxY) return;
+    
+    const i = this.index(x, y);
+    this.grid[i] += 1;
+    if (this.grid[i] > 9 && !flashGrid[i]) {
+      this.flash(x, y, flashGrid)
+    }
+  }
+
+  index(x: number, y: number): number {
+    return x + y * this.maxX;
+  }
+
+  toString(): string {
+
+    let lines = [];
+    for (let y = 0; y < this.maxY; y++) {
+      let line = "";
+      for (let x = 0; x < this.maxX; x++) {
+        line += this.grid[this.index(x, y)];
+      }
+      lines.push(line);
+    }
+
+    return lines.join("\n");
+  }
+}
+
+export default Day11;
diff --git a/functions/src/index.ts b/functions/src/index.ts
index 2470077..9fd3376 100644
--- a/functions/src/index.ts
+++ b/functions/src/index.ts
@@ -12,6 +12,7 @@ import Day7 from "./day7";
 import Day8 from "./day8";
 import Day9 from "./day9";
 import Day10 from "./day10";
+import Day11 from "./day11";
 
 
 // // Start writing Firebase Functions
@@ -38,6 +39,7 @@ export const day = {
   8: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day8(), request, response) }),
   9: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day9(), request, response) }),
   10: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day10(), request, response) }),
+  11: functions.region("europe-west1").https.onRequest((request, response) => { processDay(new Day11(), request, response) }),
 
 }
 
diff --git a/input/day/11-example.http b/input/day/11-example.http
new file mode 100644
index 0000000..48e8137
--- /dev/null
+++ b/input/day/11-example.http
@@ -0,0 +1,15 @@
+POST http://localhost:5001/advent-of-code-2021-911a8/europe-west1/day-11
+Content-Type: text/plain
+
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
+
+###
diff --git a/input/day/11.http b/input/day/11.http
new file mode 100644
index 0000000..09e962d
--- /dev/null
+++ b/input/day/11.http
@@ -0,0 +1,15 @@
+POST http://localhost:5001/advent-of-code-2021-911a8/europe-west1/day-11
+Content-Type: text/plain
+
+2524255331
+1135625881
+2838353863
+1662312365
+6847835825
+2185684367
+6874212831
+5387247811
+2255482875
+8528557131
+
+###