//一破题付出血的代价   多思考！
public static void offer(int [][]a){

       int left=,right=a.length-,low=,high=a[].length-;

       while(low<=high){

            for(int i=left;i<=right;i++){//

                System.out.print(a[left][i]+" ");

            }

            low++;

           for(int i=low;i<=high;i++){//

               System.out.print(a[i][right]+" ");

           }

           right--;

           for(int i=right;i>=left;i--){//

               System.out.print(a[high][i]+" ");

           }

           high--;

           for(int i=high;i>=low;i--){//

               System.out.print(a[i][left]+" ");

           }

            left++;

       }

    }