算法1 BFS

package dbfs;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.LinkedList;
import java.util.Queue;


class Pair{
    int x;
    int y;
    public Pair(int x, int y) {
        super();
        this.x = x;
        this.y = y;
    }

}

public class 红与黑 {

    /**
     * bfs
     * @param args
     * @throws IOException 
     */

    static int N=30;
    static int w,h;
    static boolean st[][];
    static char g[][]=new char [N][N];
    static int res;
    static int stx=0;
    static int sty=0;
    static int dx[]={-1,0,0,1};
    static int dy[]={0,1,-1,0};

    public static void bfs() {
        res=1;
        Queue<Pair> queue= new LinkedList<Pair>();
        st[stx][sty]=true;
        queue.offer(new Pair(stx, sty));

        while(!queue.isEmpty()){
            Pair pair1= queue.poll();

            for(int i=0;i<4;i++){
                int x=pair1.x+dx[i];
                int y=pair1.y+dy[i];

                if(x>=0 && x<h && y>=0 && y<w && !st[x][y] && g[x][y]=='.'){
                    queue.offer(new Pair(x, y));
                    st[x][y]=true;
                    res++;
                }

            }

        }
    }

    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
     BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));


      while(true){

          String p[]=bufferedReader.readLine().split(" ");
          w=Integer.parseInt(p[0]);//列
          h=Integer.parseInt(p[1]);//行

          if(w==0 && h==0) break;

         for(int i=0;i<h;i++){
             String s=bufferedReader.readLine();
              for(int j=0;j<w;j++){
                  char o=s.charAt(j);
                  if(o=='@'){
                      stx=i;
                      sty=j;
                  }
                  g[i][j]=o;
              }
         }
          st=new boolean[N][N];
         bfs();
         System.out.println(res);
      }
    }

}

算法2

dfs

package dbfs;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class 红与黑dfs {

    /**
     * @param args
     */
    static int N=30;
    static int w,h;
    static boolean st[][];
    static char g[][]=new char [N][N];
    static int res;
    static int stx=0;
    static int sty=0;
    static int dx[]={-1,0,0,1};
    static int dy[]={0,1,-1,0};

    public static void  dfs(int stax,int stay) {

        for(int i=0;i<4;i++){
            int x=stax+dx[i];
            int y=stay+dy[i];

            if(x>=0 && x<h && y>=0 && y<w && !st[x][y] && g[x][y]=='.'){
                st[x][y]=true;
                res++;
                dfs(x, y);
            }
        }

    }

    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
         BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));


          while(true){

              String p[]=bufferedReader.readLine().split(" ");
              w=Integer.parseInt(p[0]);//列
              h=Integer.parseInt(p[1]);//行

              if(w==0 && h==0) break;

             for(int i=0;i<h;i++){
                 String s=bufferedReader.readLine();
                  for(int j=0;j<w;j++){
                      char o=s.charAt(j);
                      if(o=='@'){
                          stx=i;
                          sty=j;
                      }
                      g[i][j]=o;
                  }
             }
             res=1;
             st=new boolean[N][N];
             dfs(stx,sty);
             System.out.println(res);

          }
          }

}