碰到边界调转方向即可

class Solution {
    public int[] printMatrix(int[][] matrix) {
         if(matrix.length==0) return new int[0];
         int m=matrix.length;
         int n=matrix[0].length;
         int res[]=new int[m*n];
         boolean vis[][]=new boolean[m+1][n+1];
         List<Integer>list=new ArrayList<>();
         int dx[]={-1,0,1,0};
         int dy[]={0,1,0,-1};
         int a=0,b=0,d=1;
         for(int i=0;i<m*n;i++){
              list.add(matrix[a][b]);
               vis[a][b]=true;
               int x=a+dx[d],y=b+dy[d];
               if(x<0||x==m||y<0||y==n|vis[x][y]){
                    d=(d+1)%4;
                    x=a+dx[d];
                    y=b+dy[d];
               }
               a=x;
               b=y;
         }
         for(int i=0;i<m*n;i++){
             res[i]=list.get(i);
         }
         return res;


    }
}