//一破題付出血的代價   多思考！
public static void offer(int [][]a){
       int left=0,right=a.length-1,low=0,high=a[0].length-1;
       while(low<=high){
            for(int i=left;i<=right;i++){//123
                System.out.print(a[left][i]+" ");
            }
            low++;
           for(int i=low;i<=high;i++){//
 
69
               System.out.print(a[i][right]+" ");
           }
           right--;
           for(int i=right;i>=left;i--){//87
               System.out.print(a[high][i]+" ");
           }
           high--;
           for(int i=high;i>=low;i--){//45
               System.out.print(a[i][left]+"
 
 ");
           }
            left++;

       }

    }

螺旋打印2D數組