diff --git a/day11/day11.cpp b/day11/day11.cpp
new file mode 100644
index 0000000..d3c8483
--- /dev/null
+++ b/day11/day11.cpp
@@ -0,0 +1,101 @@
+#include <folly/String.h>
+
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <list>
+#include <map>
+#include <numeric>
+#include <queue>
+#include <set>
+#include <vector>
+
+constexpr char EMPTY_CHAR = 'L';
+constexpr char FLOOR_CHAR = '.';
+constexpr char OCCUPIED_CHAR = '#';
+
+std::vector<std::string> readInput(const std::string &filename) {
+	std::vector<std::string> input;
+	std::string line;
+	std::ifstream file(filename);
+	while (std::getline(file, line)) {
+		input.push_back(line);
+	}
+
+	return input;
+}
+
+std::vector<char> getNeighbors(const std::vector<std::string> &state, int row, int column) {
+	std::vector<char> neighbors;
+	for (int dRow = -1; dRow <= 1; dRow++) {
+		for (int dCol = -1; dCol <= 1; dCol++) {
+			if (dRow == 0 && dCol == 0) {
+				continue;
+			}
+
+			int candidateRow = row + dRow;
+			int candidateCol = column + dCol;
+			if (candidateRow < 0 || candidateRow >= state.size() || candidateRow < 0 ||
+				candidateCol >= state.at(candidateRow).size()) {
+				continue;
+			}
+
+			char neighbor = state.at(candidateRow).at(candidateCol);
+			neighbors.push_back(neighbor);
+		}
+	}
+
+	return neighbors;
+}
+
+char applyRules(const std::vector<std::string> &state, int row, int column) {
+	std::vector<char> neighbors = getNeighbors(state, row, column);
+	char item = state.at(row).at(column);
+	int numOccupied =
+		std::count_if(neighbors.begin(), neighbors.end(), [](char neighbor) { return neighbor == OCCUPIED_CHAR; });
+	if (item == EMPTY_CHAR && numOccupied == 0) {
+		return OCCUPIED_CHAR;
+	} else if (item == OCCUPIED_CHAR && numOccupied >= 4) {
+		return EMPTY_CHAR;
+	} else {
+		return item;
+	}
+}
+
+void printState(const std::vector<std::string> &state) {
+	for (const std::string &row : state) {
+		std::cout << row << std::endl;
+	}
+
+	std::cout << " " << std::endl;
+}
+
+int part1(const std::vector<std::string> &input) {
+	std::vector<std::string> state(input);
+	std::vector<std::string> nextState(input.size(), std::string(input.at(0).size(), ' '));
+	while (state != nextState) {
+		for (int i = 0; i < state.size(); i++) {
+			for (int j = 0; j < input.at(i).size(); j++) {
+				char res = applyRules(state, i, j);
+				nextState.at(i).at(j) = res;
+			}
+		}
+
+		std::swap(state, nextState);
+	}
+
+	return std::accumulate(state.cbegin(), state.cend(), 0, [](int total, const std::string &row) {
+		return total + std::count_if(row.cbegin(), row.cend(), [](char item) { return item == OCCUPIED_CHAR; });
+	});
+}
+
+int main(int argc, char *argv[]) {
+	if (argc != 2) {
+		std::cerr << argv[0] << " <input_file>" << std::endl;
+		return 1;
+	}
+
+	auto input = readInput(argv[1]);
+
+	std::cout << part1(input) << std::endl;
+}