归并排序的实现(again)

归并排序也就是把一个数列分成两份,首先分别对2份进行排序,然后把这2份一起排序,典型的递归实现.

实现代码: MergeSort.h：

//归并排序时间复杂度：NlogN，但是由于存在

//                          for(int i=0;i!=length;++i)

//                          *first++=*(assistSpace+i);

//数据的复制需要额外的时间，减慢了排序的速度。

#ifndef ___MERGE_SORT_H

#define ___MERGE_SORT_H

namespace zk_sima

{

     template<typename Iterator ,typename Object>

     void Merge(Iterator first,Iterator middle,Iterator last,Object)

     {

         int length=last-first;

         if(length<0)

              return ;

         Object* assistSpace=(Object*)calloc(length,sizeof(Object));

         Object* pPoint=assistSpace;

         Iterator _first=first,_middle=middle;

         while(_first!=middle&&_middle!=last)

         {

              if(*_first<*_middle)

                   *pPoint++=*_first++;

              else

                   *pPoint++=*_middle++;

         }

         if(_first==middle)

         {

              while(_middle!=last)

                   *pPoint++=*_middle++;

         }

         else

              while(_first!=middle)

                   *pPoint++=*_first++;

         for(int i=0;i!=length;++i)

              *first++=*(assistSpace+i);

         free(assistSpace);

         assistSpace=0;

     }

     template<typename Iterator>

     void MergeSort(Iterator first,Iterator last)

     {

         Iterator middle=first+(last-first)/2;

         if(first+1<middle)

              MergeSort(first,middle);

         if(middle+1<last)

              MergeSort(middle,last);

         Merge(first,middle,last,*first);

     }

 

}

#endif