头条笔试

请问下大家，第二题这样什么只能过80%，提示数组越界？不可能啊
import java.util.Scanner;

/**
 * Created by forcht on 2018/8/22.
 */
public class Main {
   static int[] xt={0,0,-1,1};
   static int[] yt={-1,1,0,0};
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int n=scanner.nextInt();
        if(n<=0)return;
        int[][] map=new int[n][n];
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                map[i][j]=scanner.nextInt();
            }
        }
        int count=0;
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                if(map[i][j]==1){
                    dfs(map,i,j,n);
                    count++;
                }
            }
        }
        System.out.println(count);
    }
    static void dfs(int[][] map,int x,int y,int n){
        if(x<0||x>=n||y<0||y>=n||map[x][y]==0)return;
        map[x][y]=0;
        for(int i=0;i<4;i++){
            dfs(map,x+xt[i],y+yt[i],n);
        }
    }

}