5 files changed, 137 insertions, 0 deletions
diff --git a/2021/day11/day11 b/2021/day11/day11
new file mode 100755
index 0000000..a39baa6
--- /dev/null
+++ b/2021/day11/day11
diff --git a/2021/day11/day11.cpp b/2021/day11/day11.cpp
new file mode 100644
index 0000000..5a88b14
--- /dev/null
+++ b/2021/day11/day11.cpp
@@ -0,0 +1,115 @@
+#include <iostream>
+#include <fstream>
+#include <vector>
+#include <string>
+
+class State {
+	public: State() { iter = 0; booms = 0; }
+	int size;
+	std::vector<int> light;
+	int xytoi (int x, int y) { return x+y*size; }
+	int itox (int i) { return i % size; }
+	int itoy (int i) { return i / size; }
+	int iter;
+	int booms;
+
+	bool oob (int x, int y) {
+		if (x < 0 || x >= size) return true;
+		if (y < 0 || y >= size) return true;
+		return false;
+	}
+
+	bool calm () {
+		for (std::size_t i=0; i<light.size(); i++) {
+			if (light[i] > 9) return false;
+		}	
+		return true;
+	}
+
+	void propagate (int x, int y) {
+		for (int i=-1; i<2; i++) {
+			for (int j=-1; j<2; j++) {
+				if (!oob(x+i, y+j)) {
+					light[xytoi(x+i, y+j)]++;
+				}
+			}
+		}
+	}
+
+	void solve () {
+		for (int y=0; y<size; y++) {
+			for (int x=0; x<size; x++) {
+				int i = xytoi(x, y);
+				if (light[i] > 9) {
+					propagate(x, y);
+					booms ++;
+					light[i] = -10000000;
+					solve();
+					return;
+				}
+			}
+		}
+		if (!calm()) solve();
+	}
+
+	void step () {
+		for (int y=0; y<size; y++) {
+			for (int x=0; x<size; x++) {
+				int i = xytoi(x, y);
+				light[i] ++;
+			}
+		}
+		solve();
+		for (std::size_t i=0; i<light.size(); i++) {
+			if (light[i] < 0) light[i] = 0;
+		}	
+		iter ++;
+	}
+
+	void show () {
+		std::cout << "iter: " << iter << std::endl;
+		for (int y=0; y<size; y++) {
+			for (int x=0; x<size; x++) {
+				std::cout << light[xytoi(x, y)];
+			}
+			std::cout << std::endl;
+		}
+		std::cout << std::endl;
+	}
+};
+
+int main (int argc, char * argv[]) {
+	std::string line;
+	std::vector<std::string> lines;
+	std::ifstream f { argv[1] };
+	do {
+		std::getline(f, line);
+		if (line.size() > 1) lines.push_back(line);
+	} while (!f.eof());
+
+	State state;
+	for (auto l : lines) {
+		state.size = 0;
+		for (char c : l) {
+			state.light.push_back(std::stoi(std::string { c }));
+			state.size ++;
+		}
+	}
+
+	state.show();
+	int last = 0;
+	int iters = argc > 2 ? atoi(argv[2]) : 100;
+	for (int i=0; i<iters; i++) {
+		state.step();
+		state.show();
+
+		if (state.booms - last == 100) {
+			break;
+		}
+		last = state.booms;
+	}
+
+	std::cout << "flashes: " << state.booms << std::endl;
+
+	return 0;
+}
diff --git a/2021/day11/day11_input.txt b/2021/day11/day11_input.txt
new file mode 100644
index 0000000..d33c53b
--- /dev/null
+++ b/2021/day11/day11_input.txt
@@ -0,0 +1,10 @@
+6227618536
+2368158384
+5385414113
+4556757523
+6746486724
+4881323884
+4648263744
+4871332872
+4724128228
+4316512167
diff --git a/2021/day11/day11_input_ez.txt b/2021/day11/day11_input_ez.txt
new file mode 100644
index 0000000..03743f6
--- /dev/null
+++ b/2021/day11/day11_input_ez.txt
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
diff --git a/2021/day11/makefile b/2021/day11/makefile
new file mode 100644
index 0000000..7614d42
--- /dev/null
+++ b/2021/day11/makefile
@@ -0,0 +1,2 @@
+all day11.cpp:
+	g++ -std=c++20 -o day11 day11.cpp