Add part 2 solution for day 11

day11/Makefile

@@ -0,0 +1,15 @@
+CC=g++
+BIN_NAME=day11
+CCFLAGS=-o $(BIN_NAME) -g -std=c++17
+LDFLAGS=-lfolly
+
+.PHONY: all, clean
+
+all: $(BIN_NAME)
+
+clean:
+	rm -f $(BIN_NAME)
+
+$(BIN_NAME): day11.cpp
+	$(CC) $(CCFLAGS) $(LDFLAGS) day11.cpp
+

day11/day11.cpp

@@ -13,6 +13,8 @@
 constexpr char EMPTY_CHAR = 'L';
 constexpr char FLOOR_CHAR = '.';
 constexpr char OCCUPIED_CHAR = '#';
+constexpr int PART_1_OCCUPIED_THRESHOLD = 4;
+constexpr int PART_2_OCCUPIED_THRESHOLD = 5;
 
 std::vector<std::string> readInput(const std::string &filename) {
 	std::vector<std::string> input;
@@ -25,7 +27,15 @@ std::vector<std::string> readInput(const std::string &filename) {
 	return input;
 }
 
-std::vector<char> getNeighbors(const std::vector<std::string> &state, int row, int column) {
+void printState(const std::vector<std::string> &state) {
+	for (const std::string &row : state) {
+		std::cout << row << std::endl;
+	}
+
+	std::cout << " " << std::endl;
+}
+
+std::vector<char> getPart1Neighbors(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++) {
@@ -35,7 +45,7 @@ std::vector<char> getNeighbors(const std::vector<std::string> &state, int row, i
 
 			int candidateRow = row + dRow;
 			int candidateCol = column + dCol;
-			if (candidateRow < 0 || candidateRow >= state.size() || candidateRow < 0 ||
+			if (candidateRow < 0 || candidateRow >= state.size() || candidateCol < 0 ||
 				candidateCol >= state.at(candidateRow).size()) {
 				continue;
 			}
@@ -48,39 +58,80 @@ std::vector<char> getNeighbors(const std::vector<std::string> &state, int row, i
 	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);
+template <typename T>
+int sign(T val) {
+	// Taken from https://stackoverflow.com/questions/1903954/is-there-a-standard-sign-function-signum-sgn-in-c-c
+	return (T(0) < val) - (val < T(0));
+}
+
+/**
+ * Extend a pair in all directions it extends - e.g. (1, 0) becomes (2,0)
+ * @tparam T The type that the pair holds
+ * @param vec The vector to extend
+ */
+template <typename T>
+void extendVector(std::pair<T, T> &vec) {
+	vec.first += sign(vec.first);
+	vec.second += sign(vec.second);
+}
+
+std::vector<char> getPart2Neighbors(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;
+			}
+
+			std::pair<int, int> deltaVector(dRow, dCol);
+			char neighbor = FLOOR_CHAR;
+			// Keep projecting our ray until we hit a non floor char
+			while (neighbor == FLOOR_CHAR) {
+				int candidateRow = row + deltaVector.first;
+				int candidateCol = column + deltaVector.second;
+				if (candidateRow < 0 || candidateRow >= state.size() || candidateCol < 0 ||
+					candidateCol >= state.at(candidateRow).size()) {
+					break;
+				}
+
+				neighbor = state.at(candidateRow).at(candidateCol);
+				extendVector(deltaVector);
+			}
+
+			neighbors.push_back(neighbor);
+		}
+	}
+
+	return neighbors;
+}
+
+char applyRules(const std::vector<char> &neighbors, char seatState, int occupiedThreshold) {
 	int numOccupied =
 		std::count_if(neighbors.begin(), neighbors.end(), [](char neighbor) { return neighbor == OCCUPIED_CHAR; });
-	if (item == EMPTY_CHAR && numOccupied == 0) {
+	if (seatState == EMPTY_CHAR && numOccupied == 0) {
 		return OCCUPIED_CHAR;
-	} else if (item == OCCUPIED_CHAR && numOccupied >= 4) {
+	} else if (seatState == OCCUPIED_CHAR && numOccupied >= occupiedThreshold) {
 		return EMPTY_CHAR;
 	} else {
-		return item;
+		return seatState;
 	}
 }
 
-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) {
+int runSimulation(
+	const std::vector<std::string> &input, int occupiedThreshold,
+	std::function<std::vector<char>(const std::vector<std::string>, int, int)> getNeighbors) {
 	std::vector<std::string> state(input);
 	std::vector<std::string> nextState(input.size(), std::string(input.at(0).size(), ' '));
-	while (state != nextState) {
+	for (int count = 0; state != nextState; count++) {
 		for (int i = 0; i < state.size(); i++) {
 			for (int j = 0; j < input.at(i).size(); j++) {
-				char res = applyRules(state, i, j);
+				std::vector<char> neighbors = getNeighbors(state, i, j);
+				char res = applyRules(neighbors, state.at(i).at(j), occupiedThreshold);
 				nextState.at(i).at(j) = res;
 			}
 		}
 
+		printState(state);
 		std::swap(state, nextState);
 	}
 
@@ -89,6 +140,14 @@ int part1(const std::vector<std::string> &input) {
 	});
 }
 
+int part1(const std::vector<std::string> &input) {
+	return runSimulation(input, PART_1_OCCUPIED_THRESHOLD, getPart1Neighbors);
+}
+
+int part2(const std::vector<std::string> &input) {
+	return runSimulation(input, PART_2_OCCUPIED_THRESHOLD, getPart2Neighbors);
+}
+
 int main(int argc, char *argv[]) {
 	if (argc != 2) {
 		std::cerr << argv[0] << " <input_file>" << std::endl;
@@ -97,5 +156,6 @@ int main(int argc, char *argv[]) {
 
 	auto input = readInput(argv[1]);
 
-	std::cout << part1(input) << std::endl;
+	// std::cout << part1(input) << std::endl;
+	std::cout << part2(input) << std::endl;
 }