希尔排序算法的JAVA实现

package Utils.Sort; 

/**

*希尔排序，要求待排序的数组必须实现Comparable接口

*/

public class ShellSort implements SortStrategy

{

       private int[] increment;

       /**

       *利用希尔排序算法对数组obj进行排序

       */

       public void sort(Comparable[] obj)

       {

              if (obj == null)

              {

                     throw new NullPointerException("The argument can not be null!");

              } 

 

              //初始化步长

              initGap(obj);

  

              //步长依次变化（递减）

              for (int i = increment.length - 1 ;i >= 0 ;i-- )

              {

                     int step = increment[i];                   

                     //由步长位置开始

                     for (int j = step ;j < obj.length ;j++ )

                     {

                            Comparable tmp;

                            

                            //如果后面的小于前面的（相隔step），则与前面的交换

                            for (int m = j ;m >= step ;m = m - step )

                            {

                                   if (obj[m].compareTo(obj[m - step]) < 0)

                                   {

                                          tmp = obj[m - step];

                                          obj[m - step] = obj[m];

                                          obj[m] = tmp;

                                   }

                                   //因为之前的位置必定已经比较过，所以这里直接退出循环

                                   else

                                   {

                                          break;

                                   }

                            }

                     }

              }

       }

 

 

       /**

       *根据数组的长度确定求增量的公式的最大指数,公式为pow(4, i) - 3 * pow(2, i) + 1和9 * pow(4, i) - 9 * pow

2, i) + 1

       *@return int[] 两个公式的最大指数

       *@param length 数组的长度

       */

       private int[] initExponent(int length)

       {

              int[] exp = new int[2];

              exp[0] = 1;

              exp[1] = -1;

              int[] gap = new int[2];

              gap[0] = gap[1] = 0;

              

              //确定两个公式的最大指数

              while (gap[0] < length)

              {

                     exp[0]++;

                     gap[0] = (int)(Math.pow(4, exp[0]) - 3 * Math.pow(2, exp[0]) + 1);                      

              }

              exp[0]--;

 

              while (gap[1] < length)

              {

                     exp[1]++;

                     gap[1] = (int)(9 * Math.pow(4, exp[1]) - 9 * Math.pow(2, exp[1]) + 1);                       

              }

              exp[1]--;

              return exp;

       }

       private void initGap(Comparable[] obj)

       {

              //利用公式初始化增量序列

              int exp[] = initExponent(obj.length);

              int[] gap = new int[2];

 

               increment = new int[exp[0] + exp[1]];             

              //将增量数组由大到小赋值

              for (int i = exp[0] + exp[1] - 1 ;i >= 0 ;i-- )

              {

                     gap[0] = (int)(Math.pow(4, exp[0]) - 3 * Math.pow(2, exp[0]) + 1); 

                     gap[1] = (int)(9 * Math.pow(4, exp[1]) - 9 * Math.pow(2, exp[1]) + 1);

 

                     //将大的增量先放入增量数组，这里实际上是一个归并排序

                     //不需要考虑gap[0] == gap[1]的情况，因为不可能出现相等。

                     if (gap[0] > gap[1])

                     {

                            increment[i] = gap[0];

                            exp[0]--;

                     }

                     else

                     {

                            increment[i] = gap[1];

                            exp[1]--;

                     }

              }            

       }

}