思路

能用深搜就用深搜，代码简洁明了
宽搜比较繁琐

算法一：深搜

写法一：

    private static int[] dx={0,0,-1,1},dy={1,-1,0,0};
    private static String[] str;
    private static boolean[][] st;
    private static int w,h,sum;
    public static int dfs(int a,int b){//返回的是瓷砖数
        st[a][b]=true;
        int cnt=1;
        for(int i=0;i<4;i++){
            int x=a+dx[i],y=b+dy[i];//这里要注意是新的变量，不能是a=a+dx[i]
            if(x>=h||x<0||y>=w||y<0)continue;//下标越界
            if(str[x].charAt(y)=='#')continue;//是墙壁
            if(st[x][y])continue;//已经走过了
            cnt+=dfs(x,y);
        }
        return cnt;
    }
    public static void main(String[] args){
        Scanner scanner=new Scanner(System.in);
        w=scanner.nextInt();h=scanner.nextInt();
        int N=25;
        while(w!=0&&h!=0){
            str=new String[N];
            st=new boolean[N][N];
            int x=0,y=0;
            for(int i=0;i<h;i++){
                str[i]=scanner.next();
                if(str[i].indexOf('@')>=0){
                    x=i;y=str[i].indexOf('@');
                }
            }
            System.out.println(dfs(x,y));
            w=scanner.nextInt();h=scanner.nextInt();
        }
    }

写法二：

    private static int[] dx={0,0,-1,1},dy={1,-1,0,0};
    private static String[] str;
    private static boolean[][] st;
    private static int w,h,sum;
    public static void dfs(int a,int b){
        if(a<0||a>=h||b<0||b>=w||st[a][b]||str[a].charAt(b)=='#'){//若不满足情况则结束递归
            return ;
        }
        st[a][b]=true;//说明该点走过
        sum++;//瓷砖数加一
        for(int i=0;i<4;i++){
            int x=a+dx[i];
            int y=b+dy[i];
            dfs(x,y);
        }
    }
    public static void main(String[] args){
        Scanner scanner=new Scanner(System.in);
        w=scanner.nextInt();h=scanner.nextInt();
        while(w!=0&&h!=0){
            str=new String[100];
            st=new boolean[100][100];
            int sx=0,sy=0;
            for(int i=0;i<h;i++){
                str[i]=scanner.next();
                if(str[i].indexOf('@')!=-1){
                    sx=i;
                    sy=str[i].indexOf('@');
                }
            }
            sum=0;//每次都要初始化
            dfs(sx,sy);
            System.out.println(sum);
            w=scanner.nextInt();h=scanner.nextInt();
        }
    }

算法二：广搜

套用广搜模板即可

class Node{
    int x;
    int y;
    public Node(int x,int y){
        this.x=x;
        this.y=y;
    }
    public int getX(){return x;}
    public int getY(){return y;}
}
class Main{
    public static void main(String[] args){
        Scanner scanner=new Scanner(System.in);
        int h=scanner.nextInt(),w=scanner.nextInt();
        int[] dx={0,0,-1,1},dy={1,-1,0,0};
        while(w!=0&&h!=0){
            String[] str=new String[100];
            boolean[][] st=new boolean[100][100];
            int sx=0,sy=0;
            for(int i=0;i<w;i++){
                str[i]=scanner.next();
                if(str[i].indexOf('@')!=-1){
                    sx=i;
                    sy=str[i].indexOf('@');
                }
            }
            Queue<Node> queue=new LinkedList<>();
            queue.add(new Node(sx,sy));
            st[sx][sy]=true;
            int sum=1;
            while(!queue.isEmpty()){
                Node node=queue.poll();
                for(int i=0;i<4;i++){
                    int x=node.x+dx[i];
                    int y=node.y+dy[i];
                    if(x>=0&&x<w&&y>=0&&y<h&&str[x].charAt(y)!='#'&&!st[x][y]){
                        queue.add(new Node(x,y));
                        st[x][y]=true;
                        sum++;
                    }
                }
            }
            System.out.println(sum);
            h=scanner.nextInt();w=scanner.nextInt();
        }
    }
}