农民种地（图的搜索）

import java.util.Scanner;

/**
 * Created by m1786 on 2017/4/2.
 * 寻找一个可行解
 */
public class 农民种地 {
    static int n;
    static int m;
    static int visited;
    static boolean flag;
    static int count;
    static char a[][]=new char[4][4];
    static String str[]=new String[4];
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        while (true) {
            count=0;
            m = sc.nextInt();
            n = sc.nextInt();
            sc.nextLine();
            if(m==0&&n==0)
                return ;
            for (int i = 0; i < n; i++)
                str[i] =sc.nextLine();

            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++)
                    a[i][j] = str[i].charAt(j);
            visited=0;
            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++)
                    if (a[i][j] == 'S')
                        visited++;

            dfs(0, 0);
            if (flag){
                System.out.println("YES");
                flag=false;
            }
            else
                System.out.println("NO");



        }

    }


    static void dfs(int x, int y) {
        if (x < 0 || y < 0 || x >= n || y >= m)
            return;
        if (a[x][y] == 'S')
            return;
        if (flag) return;
        count++;
        if(count>1500)return;//递归次数限制
        a[x][y] = 'S';
        visited++;
        if (visited == m * n) {
            flag = true;
            return;
        }
        dfs(x + 1, y);
        dfs(x, y + 1);
        dfs(x - 1, y);
        dfs(x, y - 1);

        visited--;
        a[x][y] = '.';
    }
    }