9.1数组与字符串（五）——矩阵的转置

/**

 * 功能：给定一幅由N*N矩阵表示的图像，其中每个像素的大小为4字节，编写一个方法，将图像旋转90度，

 * 不占用额外内存空间。

 */

       public static void rotate( int [][] matrix , int n ){

             for ( int layer =0; layer < n /2; layer ++){

                   int first = layer ;

                   int last = n -1- layer ;

                   for ( int i = first ; i < last ; i ++){

                         int top = matrix [ first ][ i ]; //存储上边

                         matrix [ first ][ i ]= matrix [ n -1- i ][ first ]; //左到上

                         matrix [ n -1- i ][ first ]= matrix [ last ][ n -1- i ]; //下到左

                         matrix [ last ][ n -1- i ]= matrix [ i ][ last ]; //右到下

                         matrix [ i ][ last ]= top ; //上到右

                  }

            }

      }

}