http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1130

RedAndBlack.cpp

#include <iostream>
#include <set>


class Position {
	const int x, y;

public:
	Position(int x, int y) : x(x), y(y) { }

	int distance(const Position& t) const {
		return abs(x - t.x) + abs(y - t.y);
	}

	bool near(const Position& t) const {
		return distance(t) == 1;
	}

	bool operator <(const Position t) const {
		return (y == t.y && x < t.x) || y < t.y;
	}
};


class Poses : public std::set<Position> {
public:
	int erase(const Poses& p) {
		int c = 0;
		for(auto x: p){
			c += erase(x);
		}
		return c;
	}

	int erase(const Position& p) {
		return std::set<Position>::erase(p);
	}
};


int main(){
	while(true){
		int w, h;
		std::cin >> w >> h;
		if(w == 0 && h == 0){
			break;
		}

		Poses step, floor;
		for(int y=0; y<h; y++){
			for(int x=0; x<w; x++){
				char c;
				std::cin >> c;

				if(c == '.'){
					floor.insert(Position(x, y));
				}else if(c == '@'){
					step.insert(Position(x, y));
				}
			}
		}

		do{
			for(auto s: step){
				for(auto f: floor){
					if(s.near(f)){
						step.insert(f);
					}
				}
			}
		}while(floor.erase(step));

		std::cout << step.size() << std::endl;
	}

	return 0;
}